Essay: High Performance Concrete And High Strength Concrete

Concrete is today nearly 9000 years old and has undergone several changes not only in its but also in its performance and applications. From a simple beginning around 7000BC to most complicated design and application in 2004AD concrete has been used in several structures from housing to various infrastructure projects.
Concrete has played a key role in development of our planet earth in developed, developing and under developed countries. Today, development of every type needs concrete, be it in infrastructure, in industry or even in space technology and telecommunication. In the last millennium concrete had demanding requirements both in terms of technical performance and economy and yet greatly varied from architectural masterpieces to the simplest of utilities. In the past few years, many research and modification has been done to produce concrete with higher strength and durability.
Concrete is the most widely used construction material all over the world in view of its strength, high mould ability, structural stability and economic considerations. Concrete has a good future and is unlikely to get replaced by any other material on account of its ease to produce, infinite variability, uniformity, durability and economy. In the revised IS: 456-??2000 codeU5l, concrete grades are grouped into three categories viz. Ordinary Concrete (M10 toM20), Standard Concrete (M25 to M55) and High Strength Concrete (M60 to M80) Concrete will be known by many names in the next millennium. However, the extent of development of concrete will differ from country to country depending on material availability, financial affordability, specifications for the future projects and confidence imposed by the Engineers and Architects on new materials and methods.
Cement concrete is the most extensively used construction material in many countries including India. Maintenance and repair of concrete structure is a growing problem involving significant expenditure. Since the beginning of the use of concrete, strength has been regarded as the most significant and important property of concrete But it is now well recognized that the strength of concrete may deteriorate with time, as a result of a combination of various factor that may include carbonation of concrete, reinforcement corrosion, chemical attack on concrete, poor quality of materials and workmanship.

1.2 High Performance Concrete and High Strength Concrete
“High performance concrete” is used for concrete mixture which possess high workability, high strength high modulus of elasticity, high density, high dimensional stability, low permeability and resistant to chemical attack.
There is little controversy between the terms of high performance and high strength concrete. High performance concrete is also, high strength concrete but it has a few attribute specially design as mentioned above.

High performance concretes (HPC) are concretes with properties or attributes which satisfy the performance criteria. Generally, concretes with higher strengths and attributes superior to Conventional concretes are desirable in the Construction Industry. HPC is defined in terms of strength and durability.
Therefore HPC can be considered as a logical development of cement concretes in which the ingredients are proportioned and selected to. Contribute efficiently to the various properties of cement concrete in fresh as well as in hardened states.
1.3.1 Salient Features of HPC
‘ Compressive strength> 80 MPa, even up to 800 MPa.
‘ Water-binder ratio =0.25-0.35, therefore very little free water.
‘ Wide range of grain sizes.
‘ Reduced flocculation of cement grains.
‘ Densified cement paste.
‘ Endogenous shrinkage.
‘ Low free lime content.
‘ Stronger transition zone at the interface between cement paste and aggregate
‘ Discontinuous spores.
‘ Less capillary porosity.
‘ No bleeding homogeneous mix.
‘ Wide range of grain sizes.
‘ Smooth fracture surface.

1.3.2. Composition of HPC
The ingredients of HPCs are almost same as those of Conventional Cement Concretes (CCC). But, because of lower Water Cement Ratio, presence of Pozzolanas and chemical admixtures etc., the HPCs usually have many features which distinguish them from CCCs.
From practical considerations, in concrete constructions, apart from the final strength, the late of development of strength is also very important.
The High performance concrete usually contains both Pozzolanas and chemical admixtures. Hence, the rate of hydration of cement and the rate of strength development in HPC is quite different from that of conventional cement concrete (CCC).
The proportioning (or mix design) of normal strength concretes is based primarily on the w/c ratio ‘law ‘proposed by Abrams in 1918 For high strength concretes, however, all the component of concrete mixture are pushed to their limits Therefore, it is necessary to pay careful attention to all aspects of concrete production, i.e., selection of materials, mix design handling and placing. In essence, the proportioning of HPC concrete mixtures consists of three interrelated steps:
1) Selection of suitable ingredients cement, supplementary cementing materials(SCM), water and chemical admixtures,
2) Determination of the relative quantities of these materials in order to produce, as economically as possible, a concrete that has the rheological properties, strength and durability.
3) Careful quality control of every phase of the concrete making process.
1.3.3 General parameters for Ideal HPC.
‘ Due to Controlled placing and curing (High performance)
‘ Good quality of paste
‘ Low W/C ratio
‘ Optimal cement content and cementations material
‘ Sound aggregate, grading and vibration
‘ Low air content

‘ High strength
‘ Due to Controlled material quality control (Resistance to wear and deterioration)
‘ Low W/C ratio
‘ Dense, homogenous concrete.
‘ High strength
‘ Wear resisting aggregate
‘ Good surface texture
‘ Due to controlled proportions ( Resistance to weathering and chemicals)
‘ Appropriate cement type
‘ Low W/C ratio
‘ Proper curing.
‘ Alkali-resistant aggregate
‘ Suitable admixture
‘ Use of super-plasticizers, fly-ash, polymers or silica fume as admixtures
‘ Air entrainment.
‘ Due to Controlled handling ( Economy)
‘ Large maximum aggregate size
‘ Efficient grading
‘ Minimum slump
‘ Minimum cement content
‘ Optimal automated plant operation
‘ Admixtures and entrained air
‘ Quality assurance and control

1.3.4. Advantages of using HPC:
The advantages of using high strength high performance concretes often balance the increase in material cost. The following are the major advantages that can be accomplished.

‘ Reduction in member size, resulting in increase in plinth area/useable area and direct savings in the concrete volume saved.
‘ Reduction in the self-weight and super-imposed DL with the accompanying saving due to smaller foundations.
‘ Reduction in form-work area and cost with the accompanying reduction in shoring and stripping time due to high early-age gain in strength.
‘ Construction of High rise buildings with the accompanying savings in real-estate costs in congested areas.
‘ Longer spans and fewer beams for the same magnitude of loading.
‘ Reduced axial shortening of compression supporting members.
‘ Reduction in the number of supports and the supporting foundations due to the in spans.
‘ Reduction in the thickness of floor slabs and supporting beam sections which are major component of the weight and cost of the majority of structures.
‘ Superior long term service performance under static, dynamic, fatigue loading.
‘ Low creep and shrinkage
‘ Higher resistance to freezing and thawing, chemical attack, and significantly improved long-term durability and crack propagation.
‘ Reduced maintenance and repairs.
‘ Smaller depreciation as a fixed cost.

1.4 Mechanism of Concrete

Concrete is a composite material that consists essentially of a binding medium within which embedded particles or fragments of aggregates. In cement concrete, the binder (matrix of hydration products) is formed from a mixture of cement and water, known as hydrated cement paste (“HCP”). Bulk volume of concrete is contributed by aggregates. Remaining Portion constitutes of
Hydrated cement paste (“HCP”). Broadly speaking, 50 to 60 % of “hcp”is made up by Calcium-Silicate-Hydrate (C-S-H), which is also known as cement gel. Calcium Hydroxide Ca (OH) 2 contributes to about 20 to 25 % of the volume and remaining 15 to 20 % is constituted by Calcium Sulfoaluminates.
In a dry concrete mix, the voids in between the coarse aggregate, particles are filled by fine aggregates, reducing their original size. Though, cement particles occupy the space inside these smaller size voids, they cannot fill them completely. As a result, some voids remain in the matrix. When water is mixed, it fills up the remaining portion of voids, establishing continuity of capillary pores in the fresh concrete. In Normal Strength Concrete (NSC), water in excess of quantity required for hydration of cement is used. This excess water is needed for achieving workability and some portion is used in self desiccation. As the hydration progresses, hydration products actually fill the capillary pores and make them discontinuous. This is because “HCP” is of swelling type; water cement mix produces “HCP” of almost double of its original volume. Hydration process of Ordinary Portland Cement is fast at the beginning but also slows down with time.
However, the hydration product does not fill up all voids and capillary pores. In actual practice, in well-hydrated paste, voids exist either due to no filing up of the space by solid phase of ‘HCP” or due to presence of air (entrained and entrapped) during the time of mixing. The first type is capillary voids and the other one is air voids. These voids are different from gel pore. Various properties of concrete are greatly influenced by the size and of voids. The size of gel pore is so small that it does not adversely affect the impermeability characteristics of the concrete. But voids of size more than that of gel pores, adversely affect the strength and durability characteristics. Like solid and void phases, water is also present in “HCP” and they are classified depending on the degree of difficulties or ease with which it can be removed from “HCP”.
Concrete is a three-phase composite material and highly heterogeneous in nature. The first two phases are aggregates and bulk hydrated cement paste “HCP”. Third one is the transition zone which represents the interfacial region between the particles of aggregates and bulk’HCP’.The transition zone is also hydrated cement paste and exists as a thin shell around the Large aggregates This third phase contains voids of larger size and micro-cracks, the magnitude of which depend on grading of all constituent solid materials, water-cement ratio, cement content, curing conditions, degree of compaction, etc. The micro-
Cracks and the voids make the transition zone as the weakest link of the concrete composite and have detrimental effects on the properties of concrete such as strength, impermeability, etc.
The mechanism, which leads to this modification, has basically three components,
‘ Reaction mechanism among the ingredients
‘ Physical process
‘ Curing
Reaction Mechanism is principally based upon chemical reaction among the ingredients and related physical phenomenon. Physical process results in creating conducive condition for reaction mechanism to take place appropriately for imparting the desired attributes of the concrete mix both at fresh and hardened state. Curing maintains the satisfactory condition so that the reaction mechanism can be completed to the desirable state. Therefore, reaction mechanism among the ingredients is the basic component of the mechanism for developing strength Concrete, while physical process and curing are supportive ones.

1.4.1 Reaction Mechanism among Ingredients
Three basic features of the reaction mechanism between ingredients in developing High Strength Concrete are,
‘ Hydration of Cement
‘ Influence of chemical and mineral admixtures on modifying the microstructure of concrete.
In many respects concrete seems to resemble “HCP” as a number of properties of concrete is directly developed from that of “HCP”. This makes hydration of cement is the basic features for the mechanism of HSC. Interfaces, in the structure of concrete composites, are arising out of hydration process and their characteristics greatly depend on the influence of chemical and mineral admixtures.
1.4.1.1 Hydration of cement.
Portland cement consists essentially of tricalcium and dicalcium silicates (C3S, C2S). Other Main compounds are interstitial phases like tricalcium aluminates
(C3A), tetra calcium aluminoferrites (C3AF) and a small amount of calcium sulphate (gypsum). Portland cement also contains minor compounds-and impurities such as alkali, sulphate, free lime, un reacted silica and magnesia. Their interface is not always negligible.
Two mechanisms have been proposed for the hydration of Portland cement, the through solution hydration and solid state hydration. The hydration process gradually progresses from the surface towards the center of the cement particle. It seems that the first mechanism is dominating during the early stages of hydration, while the second mechanism is active in the later stage when ionic mobility in solution becomes restricted. Whatever the mechanism responsible for hydration, availability of sufficient moisture (at least 80 % relative humidity) is essential for the progress of hydration process. Fulfilling this condition is not difficult in the first stage, but in second stage this may not always happen.
Solid phase of “HCP” consist of the hydration products of C3A, C4AF, C3S, C2S and some anhydrous cement particles. C3A reacts immediately when hydraulic cement is mixed with water and liberates heat. To retard quick hydration, gypsum is mixed; otherwise Portland cement would set quickly and become useless for most of construction work. C3A reacts with water and calcium sulphate (gypsum) and forms calcium sulfoaluminate (C6AS3H32), or known as ettringite, having needle like crystal morphology. When quantity of calcium sulfate is depleted, a meta-stable calcium mono-sulfoaluminate (C4AS3H18) having morphology of hexagonal crystal is formed. And finally the stable compound tricalcium aluminates hydrate (C3AH6), which has hexagonal plate morphology, is formed from the Mono sulfoaluminate hydrates. C4AF reacts with water in similar way but at a slower pace compared to C3A.
Hydration of C3S and C2S results in calcium silicate hydrates, whose customary notation is C-S-H, and Calcium hydroxide Ca (OH) 2. Complete hydration of C3S and C2S results in,
2C3S +6H= C-S-H + 3CH
2C2S + 4H = C-S-H + CH
Calcium Hydroxide (CH) has large crystal with distinctive hexagonal prismatic morphology with low surface area. C-S-H has layer structure with a very high surface area. In general, it is poorly crystalline and forms a porous solid, which
Exhibits characteristic of rigid gel. It has morphology of very small fibrous crystal. The pores within C-S-H are known as gel pores.C-S-H gel is principal contributor to strength. Chemical composition of C-S-H in hydrating Portland cement paste varies with water cement ratio, temperature and age of hydration.

1.4.1.2 Effect of Chemical and Mineral Admixtures on modifying the microstructure of concrete
Reduction of interfaces in the structure of concrete, minimizing the flocculation of cement particles in water and filling up of pores are important for better properties of concrete. Chemical and mineral admixtures augment the reaction mechanism to change the structure of concrete in achieving this. Optimization of the quantity of cement and mineral admixtures, and stringent characterization of ingredients also help in this direction. First one minimizes the quantity of un-reacted particles of mineral admixtures (in excess of those required for filler action).Second one helps in selecting appropriate ingredients so that reaction mechanism can take place without hindrance.
When water is mixed with cement, the cement particles tend to flocculate. As a result, only a portion of floccu1atd body gets in touch with water and hydration takes place in that portion keeping most of the other portion un-hydrated and resulting to higher degree of voids. A high range water-reducing admixture, super plasticizer creates conductive condition for complete hydration of cement by deflocculating the cement lump and making cement water mixtures as well dispersed system. This reduces the risk of anhydrous cement grain to be present in the structure of concrete and to improve the pore structure during hydration process by bringing almost all cement particles fully in contact with water. For higher setting time of concrete, set retarder is mixed with water reducing admixtures. Set retarder does not possibly change the microstructure of concrete, but delays the commencement of hydration process by forming an efficient barrier around the cement particles This barrier impedes the desolation cement ions during early stage of hydration. However, such barrier remains effective up to a certain period of time, which depends on type and concentration of the admixtures. The admixtures finally are removed from solution by being incorporated into the hydrated materials without, in all possibility, changing the compositions of hydrated products. Mineral admixture used in HSC are fine materials and of two types, reactive and inert fines.
Pozzolanas and cementitious materials are reactive fines. Pozzolanas improves the properties of concrete by means of Pozzolanas action as well as filler materials.
Pozzolanas Action
This is a chemical mechanism. Reactive silica (SiO2) of Pozzolanas reacts with the calcium hydroxide (CH), which is liberated during process of hydration and produces calcium silicate hydrate (C-S-H). Due to Pozzolanas reaction the larger size of crystal of Ca (OH) 2 converts to crystal of C-S-H, which is dense and leading to reduction of pore size.
Portland cement Reaction C3S + H = C-S-H + CH
Pozzolanas Reaction : S + CH + H = C-S-H
As a filler material:
This is a physical mechanism. Owing to its almost spherical shape and small size, Pozzolanas disperse easily in presence of super plasticizer and fills the voids between cement particles resulting in well tacked concrete mix.
Introduction of mineral admixtures in concrete mix affects the physical arrangement of the system, particularly near the aggregate surface where porosity exists. Inert fines act as a filler material only. The Pozzolanas action reduces substantially the quantity and size of CH crystals. This along with low w/cm ratio (which is a general feature of HSC-mix) improves the microstructure of transition zones and thus the preferential orientation of CH crystals is considerably reduced. All these result in more uniform, stronger interfacial zones with less potential of micro-cracking. This is the grain refinement of “HCP” in the transition zone. Use of mineral admixtures improves the transition zone by grain refinement, which in turn improves the aggregate – “HCP” bond in part by densifying the structure of the interface zone. This leads to increase in the compressive strength by about 25 to 30%. Significant influence is achieved by reduction in w/cm value and also due to refinement of pore structures. Improvement in the transition zone structure has also substantial effect in increasing tensile strength. Major consequence of increasing the aggregate – “HCP” bond strength (or, indeed the concrete strength in general): brittleness of the concrete (HSC) also increases. This results to the decrease in the fracture energy, probably because the stress level at which extensive micro-racking begins in the transition zone is increase.

Better performance of HSC, compared to NSC, is primarily due to grain refinement leading in improvement in particle distribution and pore structure of concrete, especially at the transition zone to achieve such refinement. Physical process has strong bearing on the chemical reaction among ingredients. Sequence and time of mixing during production of the fresh concrete are important parameters of the physical process. Other construction aspects such as placement temperature, compaction during placement, etc. have significant influence on the properties of High Strength Concrete.
Influence of sequence and duration of mixing on the properties of concrete both at fresh and hardened stage. Experimental studies show that multistage mixing has beneficial effect on the properties of concrete.
1.4.3 Curing
Objective of curing is to protect the hardening concrete till it reaches a certain degree of hydration so that desired long term properties can develop in the storage or during service condition. Aim of curing is to maintain satisfactory moisture content and temperature of concrete during its early stage. These are important for the progress and successful completion of the reaction mechanism among the ingredients.
Distinct features HSC mix are high cement content, mineral admixture and low water-cement ratio. Performance of High Strength Concrete at hardened state is rather more sensitive to curing than that of NSC. All these call for adequate and appropriate curing of HSC for proper development of its properties at hardened state. Curing is the most important cstruc1ion activity in case of High Strength Concrete and also more elaborate as compared to NSC. for given level of workability, High Strength Concrete mix has lesser quantity of water-cementations material ratio compared to NSC resulting in bleeding in case of High Loss of moisture from the exposed surface of fresh concrete at early stage Would cause plastic shrinkage.
Protection against moisture loss from fresh High Strength Concrete is crucial for the development of strength as well as for durability. Again, wet curing of HSC cannot be done at very early stage because this will increase the W/C ratio adjacent to the exposed surface causing deterioration of the concrete quality. Curing of High Strength Concrete needs to be carried out in two stages: initial curing and wet curing.

Objective of the initial curing is to prevent moisture loss from the fresh concrete till the time wet curing is started. Water is not used directly during the initial curing. Initial curing maybe terminated about an hour after the final setting time of concrete. Wet curing should be commenced immediately after initial curing. Requirement of curing duration of High strength Concrete is lower than that of NSC from strength development consideration, but this has significant effect on the shrinkage of High Strength Concrete. Duration. Of about 7 10 days for wet curing are sufficient for High Strength Concrete.
1.5 Production of HSC (Critical Parameters)
Conventional concrete and High Strength Concrete differ considerably from each other. HSC is a multi-component material like conventional concrete but its components are many more than those used in ordinary concrete. Hence, special attention needs to be paid for the selection of concrete components and their proportions. It is also equally important that the production methods, i.e. mixing, handling, transporting, placing, compacting and curing, are also executed properly.
1.5.1. Selection of appropriate materials
The selection of material is a problem because cements and aggregates are available with wide variations of compositions and properties. There are no clear guidelines as to the selection of cement and aggregate types most suitable for use in High Strength Concrete. The situation is further complicated by the fact that HSC also requires use of chemical and mineral admixtures simultaneously and that there is a proliferation of these admixtures in the market with no simple rules by which one can easily make a judicious choice.
1.5.2. Selection of Mix Proportions
This is because the relationship between strength and water-cement ratio which is the backbone of mix proportioning methods for ordinary concrete mixes may not meet all the requirements of High Strength Concrete for impermeability and volume stability.
In High Strength Concrete since very low water-cement ratio are desirable, the type and dosage of mineral admixtures have a very great influence on the strength and other characteristic properties of concrete. Size, grading and type of aggregates and their proportions also have great influence on the dimensional stability of HSC and need to be carefully looked into.
In conventional mix proportioning methods, these aspects are not given a serious consideration.
1.5.3. Durability / Dimensional Stability
In ordinary concrete the main requirements are generally strength and workability. In High Strength Concrete besides strength and workability requirement other characteristics have to be given equal if not more importance. In order to optimize characteristics such as long term durability in a given environment and dimensional stability, extensive testing program may be necessary.
1.5.4Sequence of Mixing Component Materials
The fourth and final difficulty in High Strength Concrete is to finalize sequences in which the component materials are to be added during the mixing operation, the efficiency of the mixture, the method of transportation and placement and most important of all curing technology. The above steps of concrete production are often not given due importance in ordinary concrete but they cannot be overlooked in High Strength Concrete as they have considerable influence on the microstructure and properties of the ultimate product.

2.2 Introduction
A water reducing chemical, as the name implies, is used to reduce the water content of a concrete mixture while maintaining a constant workability. The resultant effect of the reduced water content is the increased strength and durability of concrete. However, water reducers may also be employed to ‘plasticize’ the concrete, i.e. make concrete flow able. In this case, the water content (or water to cement ratio) is held constant, and the addition of the admixtures makes the concrete flow better, while the compressive strength (which is a function of the water to cement ratio), and is not affected. Another use of water reducers is to lower the amount of cement (since water is proportionately reduced) without affecting both strength and workability. This makes the concrete cheaper and environmentally friendly, as less cement is consumed.
Water reducers are classified broadly into two categories: (1) Normal and (2) High range. The normal water reducers are also called ‘plasticizers’, while the high range water reducers are called ‘super plasticizers’. While the normal water reducers can reduce the water demand by 5 ‘ 10%, the high range water reducers can cause a reduction of 15 ‘ 40%.
Water reducing chemicals are generally supplied as liquid formulations, with the active solids content in the range of 30 ‘ 40%. Normal water reducers are typically used at dosages of 0.3 ‘ 0.5% liquid by weight of cement. At higher dosages, there is a danger of excessive retardation, bleeding, and air entrainment. High range water reducers do not have these problems and are capable of being used at higher dosages of 0.7 ‘ 1% (or more) liquid by weight of cement.
2.3 Characteristics of the different plasticizer.
Used at high dosages, Lignosulphonate are capable of producing high range water reduction. However, a major problem with the use of Lignosulphonate as super plasticizers is the excessive retardation and air entrainment in concrete. Modified Lignosulphonate as super plasticizers lead to concrete with lesser variation in properties.
Sulphonated salts of melamine formaldehyde condensates are good to achieve a high initial slump. However, due to their poor slump retention characteristics, they are unsuitable for long haul applications, and more particularly for ready Climates. However, SMFs are not widely used in India owing to the poor cost-competitiveness compared to SNF.
Sulphonated salts of naphthalene formaldehyde condensates possess all the necessary characteristics to make them suitable for hot weather concreting. Mainly, these possess good slump retention characteristics, enabling their use in ready mixed concrete where long hauls are common. Slump retention characteristics are also improved by blending SNF with Lignosulphonate, which is not possible in the case of SMF. The cost of SNF is also low; making it the most used super plasticizer in India and around the world. However, the maximum incompatibility issues arise with SNF, and these will be discussed at length later in this report.
Polycarboxylates and acrylic copolymers are the most effective of all the chemicals. These can cause a reduction in water content of as much as 40%. Thus, they are highly preferred to make high and ultra high strength concrete, where the w/c may be as low as 0.20. Generally, these chemicals exhibit excellent slump retention characteristics and do not cause any delay in the gain
Class Origin Structure (typical repeat unit) Relative cost
Lignosulphonate Derived from neutralization, precipitation, and fermentation processes of the waste liquor obtained during production of paper-making pulp from wood 1
Sulphonated melamine formaldehyde (SMF) Manufactured by normal resinification of melamine – formaldehyde 4
Sulphonated naphthalene formaldehyde (SNF) Produced from naphthalene by oleum or SO3 sulphonation; subsequent reaction with formaldehyde leads to polymerization and the sulphonic acid is neutralized with sodium hydroxide or lime 2
Polycarboxylic ether (PCE) Free radical mechanism using peroxide initiators is used for polymerization process in these systems 4
Table 1. Super plasticizing chemicals

Of strength of the concrete. The downside of these admixtures is their high cost. However, as stated earlier, for the same category of concrete (workability) PCEs can work at lower dosages than SNFs and Lignosulphonate. Thus, the overall cost of concrete is not affected. Only in the case of special concretes such as self compacting concrete (SCC), the use of PCEs can substantially increase the concrete cost. It must be stated, though, that making good quality SCC without these latest generation super plasticizers is almost impossible. Limited experience with these chemicals indicates that they work well at low water to cement ratios, and exhibit fewer compatibility problems compared to SNF.
2.4 Mechanism of action of water reducers.
Water-reducing chemicals belong to a group of chemicals known as ‘dispersants’. The action of the dispersant is to prevent the flocculation of fine particles of cement. These dispersants are basically surface-active chemicals consisting of long-chain organic molecules, having a polar hydrophilic group (water-attracting, such as -COO-, -SO3-, -NH4+) attached to a non-polar hydrophobic organic chain (water-repelling) with some polar groups (-OH). The polar groups in the chain get adsorbed on the surface of the cement grains, and the hydrophobic end with the polar hydrophilic groups at the tip project outwards from the cement grain. The hydrophilic tip is able to reduce the surface tension of water, and the adsorbed polymer keeps the cement particles apart by electrostatic repulsion (The grinding of cement results in the ground particles having a surface charge (zeta potential). The adsorption of the admixture leads to a decrease of the zeta potential, and eventually causes like charges (negative) on the cement particles). With the progress of hydration, the electrostatic charge diminishes and flocculation of the hydrating product occurs.
Electrostatic repulsion depends on the composition of the solution phase and the adsorbed amount of the SP (greater the adsorption, better the repulsion) [Nakajima and Yamada, 2004]. On the other hand, steric repulsion depends on the length of main chain, length and number of side chains [Sugiyama et al., 2003].
In the case of PCE based admixtures, for fluidity retention, the main chain should be short, with large numbers of long side chains [Sugiyama et al., 2003]. Because of the steric repulsion mechanism, PCEs are generally more effective than the sulphonate based admixtures, and generally do not experience much problems at low water to cement ratios. However, they are more sensitive to overdosing, and can lead to problems like excessive air entrainment and retardation.
Additional mechanisms of SP action include dispersion of cement particles by reduction in surface tension of mixing water and a decrease in frictional
Resistance because of the line-up of linear polymers along the concrete flow direction and lubrication properties produced by low molecular weight polymers [Uchikawa et al., 1995].

Figure 1. Mechanism of electrostatic repulsion (top) and steric hindrance (bottom)
Apart from affecting the early age physical properties of concrete, SPs can also cause some changes in the morphology of hydration products. Size of portlandite crystals decreases with addition of admixtures [Grabiec, 1999]. Ettringite in the presence of SPs (at high dosage) crystallizes in small and massive clusters rather than the conventional needle shape [Hanna et al., 2000; Prince et al., 2002]. In general, SPs improve rheological properties by yielding smaller hydrate particles and preventing hydration products from bridging neighboring cement particles. There is also a difference in porosity and pore size distribution of super plasticized concrete compared to normal concrete. Higher numbers of smaller pores are produced in super plasticized mixtures,
Which could have an influence on the degree of shrinkage? While the mechanism of action of water-reducing chemicals is reasonably well-established, there still exist gaps in the comprehension of why occasionally these chemicals do not work as intended. This is because the problem of cement-super plasticizer compatibility has many dimensions to it. On the one hand, there is the composition of the water reducer, as discussed above. On the other end of the spectrum is the composition of cement, particularly the relative proportions of C3A, alkalis and C3S in the cement. In addition, the type of gypsum available (gypsum, hemihydrates, or anhydrite) has an important role to play. The fineness of cement could also affect its compatibility with a particular admixture. Each of these factors influences the phenomenology of cement-water reducer interaction.

3.1 Introduction
Lignosulphonate salts of sodium and calcium, hydroxycarboxylic acids (citric and gluconic acid) and carbohydrates (corn syrup and dextrin) are examples of normal water reducers. All the super plasticizers are water soluble polymers. As for other polymers, the behavior of super plasticizers is also a function of the structure and the degree of polymerization.
Lignosulphonate are generally regarded as ‘1st generation’ super plasticizers, while the sulphonated formaldehyde condensates are called ‘2nd generation’, and the polycarboxylates and polyacrylates are termed as 3rd generation super plasticizers. Currently, the most widely used super plasticizers are the sulphonated formaldehyde condensates. However, the beneficial effects of polycarboxylates are ensuring a gradual shift towards these chemicals.
In terms of costs, polycarboxylic ether and sulphonated melamine formaldehyde are almost equal (taken on an effective solids basis), sulphonated naphthalene formaldehyde is about half the cost of the PCE, while Lignosulphonate is the cheapest (about ?? of PCE). However, in terms of effectiveness to achieve a specific workability of the concrete, the amount of PCE required is much lesser than SNF or Lignosulphonate. Thus, the overall cost of a normal plasticized concrete would not be affected based on the choice of the chemical (with the exception of SMF, which are more expensive considering the desired workability of concrete).
3.2 Source of Lignosulphonate.
The raw material for production of Lignosulphonate is trees. Trees can be grouped as softwood and hardwood. The wood substance on trees is composed of different cells, which give the mechanical strength to the trees. The wood cell consists mainly of cellulose, hemicelluloses and lignin. A simplified picture describes a skeleton of cellulose surrounded by other substances functioning as matrix (hemicellulose) and encrusting (lignin) materials. Wood can be separated into two categories of molecules: macromolecules and low molecular weight substances. Macromolecular substances:
‘ Cellulose (45 %)
‘ Hemicellulose (20-25 %)
‘ Lignin (softwood 27-37 %, hardwood 16-29 %)
The properties and chemical composition of lignin and hemicellulose differ in softwood and hardwood, while the cellulose is a uniform component of all wood.

Low molecular weight substances:
‘ Extractives (terpenes, alcohols, aliphatic acids, aromatic compounds,|)
‘ Mineral components (K, Ca, Mg, Si,)
3.3 Structure of Lignosulphonate.
Because it is not possible to isolate native lignin from wood without degradation, the true molecular mass of lignin in wood is unknown. It is important to keep in mind, however, that the term “lignin ‘or “Lignosulphonate” normally refers to a mixture of substances having similar chemical composition but structural differences. The sulfonate groups (S03.) that are introduced during the pulp cooking, i.e. dissolving the lignin from the wood.

Lignosulphonate can be classified as hydrophobic polyelectrolytes. This description refers to the fact that the polymer is dependent on its ionized groups for water solubility. Lignosulphonates are in that respect similar to sulfonated synthetic polymers used as water reducing admixtures, e.g.sulfonated
Naphthalene formaldehyde condensate (SNF) and sulfonated melamine formaldehyde condensate (SMF), which also are intrinsically hydrophobic polymers. Compared to common linear polymers there is a significant complexity inherent to the chemical structure of Lignosulphonates.

The role of the relative content of different functional groups is more difficult to predict than configurationally differences, and the effect of which may be expected to differ from system to system. An important phenomenon for the function of Lignosulphonate in cementitious systems is that a low ratio of sulfonate to phenolic and carboxylic groups leads to a reduced stability of lignosulphonate in alkaline solutions rich in calcium ions. Because of this effect precipitation of Ca-lignosulphonate complexes in alkaline solution occur with several families of sulfonated lignin’s, including oxy lignin’s, Kraft lignin’s, and some hardwood lignin’s.

3.4 Production of Lignosulphonates.

Pulp has basically been produced from wood. Pulp is predominantly used for papermaking but also processed to various cellulose derivatives. The main purpose of the pulping processes is to liberate the fibers, which can be accomplished either chemically or mechanically or by combining these two types of treatments. Only the chemical pulping processes will be treated here, since they are the basis for Borregaard LignoTech’s raw material and thus also the basis for production of lignosulphonate.

The principal behind the chemical pulping processes is to liberate the cellulose by dissolving other macromolecules like hemicellulose and lignin into the cooking liquor.

Conditional typical of acid sulphite pulping (140 DC, pH 1-2) results in effective delignification. Ca hydrogen sulphite is the cooking chemical in the Borregaard process. Since Ca is the base all salts produced are Ca salts. Other bases used in sulphite pulping are Mg, Na or NH4.

Two reactions during the sulphite cook are of importance in the formation of Lignosulphonates fragmentation and sui phonation. These reactions are the main reaction, but there will also be other like condensation. The result of the reactions is water-soluble sulfonated lignin (Lignosulphonate). The hemicellulose (sugar polymer) will under the acidic sulphite conditions be hydrolyzed to monomer components like D-mannose, D-glucose, D-xylose, L-arabinose, D-galactose and L-rhamnose (reducing sugars) in the cooking liquor. This means that the Lignosulphonate intermediate (the liquor after removal of the pulp) contains sulfonated lignin fragments of different molecular size (the lignosulphonate),sugar monomers, inorganic salts and small amounts of extractives from wood.

For this project work following literatures are referred for the studies These literatures are classified as journal, documents collected from web and some special literatures. Abstracts of some literature are included here for review

1) Per Just Andersen ‘Superior concrete mix design with workability optimized gradation and fixed paste volume’ Jan 6, 2011
Methods for design-optimization of concrete compositions having workability optimized gradation and fixed cement paste volume are disclosed. In particular, the methods allow for designing and manufacturing of concrete compositions having target compressive strengths and slumps and having a fixed volume of cement paste based on target compressive strengths and/or target slump amounts using improved methods that more efficiently utilize all the components from a performance standpoint.

2) Mario Collepardi, Enco, Engineering Concrete, Ponzano Veneto (Italy)’Admixtures-Enhansing concrete process’

Super plasticizers are the most important admixtures enhancing concrete
Performance. The development of new super plasticizers during the last decades has determined the most important progress in the field of concrete structures in terms of higher strength, longer durability, lower shrinkage and safer placement particularly in elements with very congested reinforcement. The progress from sulphonated polymer to polycarboxylatehas resulted in higher water reduction at a given workability and lower slump loss. More recently poly-functional super plasticizers have been developed which are able to completely keep the initial slump for at least 1 hr without any retarding effect on the early strength. Moreover, multi-purpose and poly-functional super plasticizers have been invented which are able to reduce drying shrinkage.

3) Salahaldein Alsadey ‘Effects of Super plasticizing Admixture on Properties of Concrete’.

In recent decades, tremendous success has achieved in the advancement of chemical admixtures for Portland cement concrete.The effect of super plasticizer (SP) on properties of fresh and hardened concrete has studied; the properties of concrete inspected are compressive strength and slump test, hence,
an experimental investigation conducted to determine the optimum dosage for the admixture and to study the effect of over dosage of the mentioned admixture, together with one control mixed. The difference between concrete mixes comes from dosages of admixture, which used at amounts 600, 800, 1000, and 1200 ml/100kg of cement were prepared. However, compressive strength is improved by dosage 1.0 % of SP after 28 days curing is 55 N/mm2 ,which is higher than that of control concrete, the optimum amount of admixture must be 1 %. Over dosage of SP found to deteriorate the properties of concrete with indication of lower compressive strength.

4) Venu Malagavelli, Neelakanteswara Rao Paturu’ Strength and Workability Characteristics of Concrete by Using Different Super Plasticizers’

Concrete, a composite material made with cement, aggregates, admixtures or super plasticizers and water comprises in quantity the largest of all man-made materials. Although aggregates make up three fourths of the volume of concrete, the active constituent of concrete is cement paste. The properties and performance of concrete are largely deter-mined by the properties of the cement paste. Super plasticizers in concrete confer some beneficial effects such as acceleration, retardation, air entrainment, water reduction, plasticity etc., and these effects are due to their action on cement. The scientists are mainly concentrating to develop the specialized concretes, to enhance the service life of the buildings, and to provide satisfactory performance under aggressive environments. In the present experimental investigation M30 concrete is used as control mixture with four different super plasticizers namely SNP (Sulphonated Naphthalene Polymer) 1, SNP 2, SNP 3 and SNP 4. Strength of modified concrete is compared with the normal concrete i.e. without super plasticizer. The results show that the significant improvement in the strength and workability of modified concrete.

5) Automatics vicamatic apprartus for cement setting time:

A fully automatic vicamatic instrument that can test the time of the cement condensing which comprises a stand , a body, a head, a turntable , a shift institution, an electric power source, a needle-rubbing institution, a heat and wet-preserving box , a control system , displaying and typing system. The utility model is characterized in that a test needle and raising or falling shift sensory institution is arranged within the head of the instrument, wherein the test needle is connected with the floor, and on the turntable is provided with a electrical sampling-gathering terminator that is respectively connected with the signal voltage input end and stable voltage input end via the series resistor. When the mental test model and cement serum and the test needle of the
sampling end-gathering end positioned on the turntable conducts electricity, the signal is received. The utility model can imitate the whole process of manual operation and is convenient to be operated and has high test accuracy. The results of the test is automatically calculated and analyzed and the utility model can is automatic test instrument that can print out the test results and based on this, the utility model can research and develop a plurality of groups of large cement testing vicamatic instrument according to the characteristics of the test.

6) Anthony E. Cerkanowicz, Chai Jaturapitakkul, John W. Liskowitz, Methi Wecharatana, ‘Method for predicting the compressive strength of concrete and mortar containing fly ash’

The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction. The invention also relates to hardenable mixtures comprising cement and fly ash which can achieve greater compressive strength than hardenable mixtures containing only concrete over the time period relevant for the construction. In specific embodiments, concrete and mortar containing about 15% to 25% fly ash as a replacement for cement, which are capable of meeting design specifications required for building and highway construction, are provided. Such materials can thus significantly reduce construction costs.

5.1 Selection of materials.
For developing concrete mix, it is important to select proper ingredients, evaluate their properties and understand the interaction among different materials. HSC will normally contain not only Portland Cement, Aggregate and Water, but also Superplasticisers and Supplementary Cementing Materials.
The ingredients used for this Dissertation work are same as that used for the normal concrete ordinary Portland Cement, Coarse and Fine Aggregates, Water and Chemical Admixture – except for Silica Fume and Fly ash which is generally not used in conventional concrete.
5.1.1. Ordinary Portland Cement
There are two requirements that any cement must meet: (i) it must develop the appropriate strength; and (ii) it must exhibit the appropriate rheological behaviour.
In this project Work, the Cement selected is Ordinary Portland 53 Grade Cement. The technical information is as follows:
Brand Name : Sanghi Cement 53 Grade O.P.C.
Conforming IS Cods : IS: 12269-1976
The Laboratory Test Results are attached herewith. The Tests includes (i) Fineness of Cement, (ii) Standard consistency, (iii) Compressive Strength of Mortar Cubes sq cm for O P C The test results are above the limiting value.

Property Average value for OPC used in present investigation Standard value for OPC
Specific gravity 3.15 –
Consistency (%) 32% –
Initial setting time(mm) 48 >30
Final setting time(mm) 225 <600
Fineness By Dry sieving 8% <10%
Compressive strength (N/mm2)
3-days 28.7 >27
7-days 39.63 >37
28-days 55.94 >53
Table 5.1 Properties of Cement
5.1.1.1. Test to find standard Consistency of Cement
Weight of Cement: – 400
Initial Reading (when needle touches the top surface of mould): – 40mm
Observation: –
Sr. No. Percentage of
Water to be added
(%) Water (ml) Penetration from
bottom (mm)
1. 27 112 25
2. 28 116 17
3.. 29 120 13
4. 30 124 9
S. 31 128 8
6. 32 132 6
Table 5.2 Measurement of Penetration for Standard Consistency of Cement Paste.

Result: -The Standard Consistency of the cement is 32%.

Figure 5.1 Vicat Apparatus (Conforming to IS 4031-1968)

5.1.1.2. Test to find setting time of cement
Weight of Cement = 400gm
Water =0.85*31.5*400/100=107.l ml

Time (minutes) Penetration (mm)
0 40
20 38
30 37
40 36
45 35.5
48 35
Table 5.3 Measurement Of Penetration For Setting Time Of Cement

RESULT:
Initial setting time of cement =48 mm.
Final setting time of cement = 225 mm.

5.1.1.3 Determination of compressive strength of cement cube.
Temperature of Lab.: – 33??C
Cement – Standard Sand Proportion: – 1: 3
Weight of Cement: – 200gm
Weight of Standard Sand: – 600gm (conforming to IS: 650-1966)
Consistency of Cement: – 33%
Water- (P/4+3%) of combined mass =90 ml.
–

Observation: –
Sr. No. No. of Days Comp.
Strength
(kg/cm2) Average Comp.
Strength
(kg/cm2) Value accorading to
IS: 4031-1968
1. 3Days 280
270
270 273.33 160
2. 7Days 344
340
368 350.67 220
3. 28Days 528
543
538 536.33 530
Table 5.4 Cement Mortar Cube Strength

5.2 Aggregates
The aggregate properties that are most important with regard to high strength concrete are: article shape, particle size distribution, mechanical properties of the aggregate particles, and possible chemical reactions between the aggregate and the paste which may affect the bond. Unlike their use in ordinary concrete, where we rarely consider the strength of the aggregates, in high strength concrete the aggregates may well become the strength limiting factor. Also, since it is necessary to maintain a low w/c ratio to achieve high strength, the aggregate grading must be very tightly controlled.
5.2.1 Coarse Aggregate:
For high strength concrete, the coarse aggregate particles themselves must be strong. From both strength and rheological considerations, the coarse aggregate particles should be roughly equi-dimensional; either crushed rock or natural gravels, particularly if they are of glacial origin, are suitable. In addition, it is important to ensure that the aggregate is clean, since a layer of silt or clay will reduce the cement-aggregate bond strength, in addition to increasing the water demand.
5.2.2 Fine Aggregate:
The fine aggregate should consist of smooth rounded particles, to reduce the water demand. It is recommended that the grading should lie on the coarser side of the limits, a fineness modulus of 3.0 or greater is recommended, both to decrease the water requirements and to improve the workability of these paste-rich mixes. Of course, the sand too must be free of silt or clay particles.
In this Dissertation Work, the coarse aggregate selected is of 20mm and 10mm down crushed rock type and fine aggregate of natural river sand locally available. The Laboratory Tests Results are attached herewith. The Tests includes (i) Specific Gravity and Water Absorption, (ii) Bulk Density, and (iii) Fineness Modulus.
5.23 Test on fine and coarse Aggregate:
1 Test for Specific Gravity
Weight: – Fine Aggregate (Sand): 500gm, Coarse Aggregate: 1000gm

Observation: –
DESCRIPTION SAMPLE:1 SAMPLE: 2
Weight A: Weight of Jar + Water + Sample. 1.701 2 545
Weight B: Weight of Jar + Water 1.388 2.225
Weight C Surface Dry Weight
(After 24 hrs.) 0.590 0.584
Weight D: Oven Dry Weight(100 to 110??C for 24 hrs.) 0.493 0.487
Specific Gravity [C / (B-A+C)} 267 2.676
Moisture Absorption: [{(C-D) / D}x100] 8.304% 10.759%
Table 5.5 Observations for Coarse Aggregate (20 mm down)

Specific gravity of Sand: 2.67
Specific gravity of Aggregate (10): 2.72 and (20):2.78

2.) Test for Bulk Density of Aggregates
Observation: –
For Fine Aggregate (Sand):
Weight of compacted sample + empty weight of container = 11.50kg
Weight of sample + empty weight of container = 11.20kg
For Coarse Aggregate:
Weight of compacted sample + empty weight of container = 34.80kg .
Weight of sample + empty weight of container = 34.10kg

Calculation: –
Bulk Density = Net weight of Aggregates in kg / Capacity of container in Liter.
For Fine Aggregates: For Coarse Aggregates:
Compacted Bulk Density: = 1453 kg/m3 Compacted Bulk Density: = 2000 kg/m3
Loose Bulk Density: = 1470 kg/m3 Loose Bulk Density: = 1900 kg/m3

3) Test for finding Fineness Modulus of Aggregates
Sieve Sizes: 40mm, 20mm, 10mm, 4.75mm, 2.36mm, 1.18mm, 600?? 300??,150?? 75?? Pan
Weight of Aggregate: Coarse Aggregate (CA-I(10MM),
CA-II(20MM)): Each 5000gm,
Fine Aggregate (Sand): 2000gm
Is sieve size Weight
retained (kg) % weight
retained Cumulative %
weight retained % passing
40mm 0 0 0 100
20mm 1.346 26.92 26.92 73.08
10mm 2.866 57.32 84.24 15.76
4.75mm 0.65 13 97.24 2.76
2.36mm — — 9724 2.76
1.18mm — — 97.24 2.76
600?? — — 97.24 2.76
300?? — — 97.24 2.76
150?? — — 97.24 2.76
‘= 694.6
75?? — — 2.76
Pan 0.138 2.76 0
Table 5.6 Sieve Analysis For Fineness Modulus of coarse agg. (20mm)
Fineness Modulus of Coarse Aggregate (20 mm down) F.M.
= 694.6/ 100=6.946

Is sieve size Weight
retained (kg) % weight
retained Cumulative %
weight retained % passing
40mm 0 0 0 100
20mm 0 0 0 100
10mm 3.02 60.4 60.4 39.6
4.75mm 1.97 39.4 99.8 0.2
2.36mm — — 99.8 0.2
1.18mm — — 99.8 0.2
600?? 99.8 0.2
300?? — — 99.8 0.2
150?? — — . 99.8 0.2
‘= 659.2
75?? — —
Pan 0.139 100 0
Table 5.7 Sieve Analysis For Fineness Modulus of coarse agg. (10mm)
Fineness Modulus of Coarse Aggregate (10 mm down)
F.M. = 659.2/ 100 = 6.592

Is sieve size Weight
retained (kg) % weight
retained Cumulative %
weight retained % passing
40mm 0 0 0 100
20mm 0 0 0 100
10mm 0 0 0 100
4.75mm 0.172 8.6 8.6 91.4
2.36mm 0.208 10.4 19 81
1.18mm 0.430 21.5 40.5 59.5
600?? 0.568 28.4 68.9 31.1
300?? 0.472 23.6 92.5 7.5
150?? 0.120 6 98.5 1.5
‘= 287
75?? 0.026 13 99.8 0.02
Pan 0.004 0.8 100 0
Table 5.8 Sieve Analysis For Fineness Modulus (Sand)
Fineness Modulus of Fine Aggregate (Sand) F.M.= 287/ 100= 2.87
Fineness Modulus of fine aggregate: 2.87
Fineness Modulus of coarse aggregate(20mm): 6.94
Fineness Modulus of coarse aggregate(l0mm) 6.59
Conclusion :- Specified limits for Fineness Modulus of Sand
Fine Sand: F.M.: 2.2-2.6
Medium Sand: F.M.: 2.6-2. 9
Coarse Sand F.M.: 29-32
From the test we can say that Fine Aggregate (Sand) is Medium Saud and it is Conforming to Zone II grading as per IS: 383-1970.

 

6.1. Basic principles
High Strength Concrete Mix Design method has been developed by Emtroy and Shacklock. of the Cement and Concrete Association. In this method only one major modification is necessary as compared to the method of design of medium strength mixes (Road Research Note No. 4) i.e. information on the required degree of workability and the type and maximum size of the aggregate must be available before the w/c ratio can be selected. The method is confined to high strength concrete mixes made out of Ordinary or Rapid-Hardening Portland Cement and two types of coarse aggregate of two maximum sizes 20mm & 10mm in combination with natural sand, The other special features of high strength concrete mix design are (a) In the degree of workability, the category of high degree of workability is removed and extremely low workability is introduced. (b) Average design strength, at different ages for Ordinary Portland Cement and Rapid Hardening Cement and for crushed granite and irregular gravel coarse aggregate, is plotted against an arbitrary “Reference Number”. (c) Water/Cement ratio is not directly obtained from a graph connecting average compressive strength and w/c ratio but it is obtained from a graph connecting reference number, degree of workability and size of coarse aggregate.
For designing mixes of medium compressive strength, i.e. up to 35N/mm2 , it is assumed the compressive strength of fully compacted concrete at given age to be dependent water-cement ratio of the mix. However, it has been found that as the strength of the concrete increases, the properties of the mix are not so simply related and, particularly, that the compressive obtained with a given water-cement ratio is affected by the type of Aggregate used and the richness of the mix. The methods of mix design used for medium strength concrete cannot be, therefore, expected to lead to an accurate estimate of the :mix proportions for concrete under all conditions. While the compressive strength of concrete is not as easily established in high strength mixes as in those of lower strength, other aspect can be simplified. Further, rich mixes of low workability are needed for high concrete.

There is no clear-cut demarcation in the range of strength which can be recommended forarising the methods of designing medium strength and high strength mixes for all conditions, because the transition is gradual. However, as a guide in designing mixes for a specified strength at the usual ages of 7 and 28 Days, the method for high strength mixes should be adopted if the average compressive strength is to be above about 35N/mm2. The factors which are included in high strength mix design may become important at somewhat lower strengths if the age at which the strength required is lower or if the workability of the mix is usually low.
As said before, the compressive strength of high strength mixes not only depends on the w/c ratio but also varies considerably with the richness of the mix and types of aggregates. Furthermore, the workability may vary with the type and even the consignment of cement and may be higher for concrete made with crushed coarse aggregate than for that made with irregular gravel coarse aggregate. Since the properties of materials have such an important effect, suitable mix proportions cannot be estimated very closely from the available data nor can standard mixes be prepared for high strength concrete The need for trial mix is more in case of high strength concrete than medium strength concrete.
It appears that for given material, the compressive strength increases as the w/c ratio is reduced, as would be expected; but for a given w/c ratio, the strength decreases as the mix is made richer. An increase in strength due to lowering the w/c ratio, which also reduces the workability, therefore, tends to be cancelled if the mix is then made richer to maintain the original workability.

6.2 IS Method of mix design
The Bureau of Indian Standards, recommended a set of procedure for design of concrete mix . The procedure is based on the research work carried out at national laboratories. The design procedures are covered in IS: 10262-1982. The IS recommended guidelines for mix des include the design of normal concrete mixes (non-air-entrained) for both medium and high strength concretes.

6.3 Design steps:
Step-1 Target strength for mix design
The target average compressive strength (fck) of concrete at 28 days is given by
Fck’=fck + t x S
where
Fck’= target average compressive strength at 28 days
fck = characteristic compressive strength at 28 days
s= standard deviation table 6.2
t= a statistical value, depending upon the accepted proportion of low results and the number of tests; for large number of tests, the value of t is given in table 6.1

. TABLE 6.1 VALUES OF t
Accepted proportion
of low results Value of t
1 in 5 0.84
1in l0 – 1.28
1 in 15 1.50
1 in 20 1.65
1 in 40 . 1.86
1 in 100 2.33

TABLE 6.2
STANDARD DEVIATION(S) (IS : 456-2000)
Grade of concrete Assumed standard deviation N/mm2
M 10 3.5
M 15
M 20 4.0
M 25
M 30
M 35 5.0
M 40
M 45
M 50

Step-2 Selection of water-cement Ratio :
Since different cements and aggregates of different maximum shape and other characteristics may produce concretes of differ same free water-cement ratio, the relationship between strength and preferably be established for the materials actually to be used. the preliminary free water-cement ratio (by mass) corresponding days may be selected from the relationships shown in fig. 6.1.
Alternatively, the preliminary free water-cement ratio (by mass) corresponding to the target average strength may be selected from the relationships shown in fig. 6.2 using the curve corresponding to the 28 days cement strength to be used for the purpose. However, this will need 28 days for testing of cement.

FIG. 6.1

FIG. 6.2
Step-3 : Estimation of Air-content
Approximate amount of entrapped air to be expected in normal (non-aft-entrained) concrete is given in table 6.3.

TABLE 6.3
APPROXIMATE AIR CONTENT
Nominal maximum
size of aggregate Entrapped air, as percentage
of volume of concrete
(mm) (%)
10 3.0
20 2.0
40 1.0
Step-4 Selection of water content and fine to total aggregate ratio:
For the desired workability, the quantity of mixing water per unit volume of concrete and the ratio of fine aggregate (sand) to total aggregate by absolute volume are to be estimate from table 6.4 and table 6.5 as applicable, depending upon the nominal maximum size and type of aggregates.
TABLE 6.4
APPROXIMATE SAND AND WATER CONTENTS PER CUBIC METRE OF CONCRETE FOR GRADES UP TO M 35
w/c = 0.60, workability = 0.80 C.F
Nominal
maximum size
of aggregate (mm) Water content* per
cubic metre of concrete
(kg) Sand as percentage of
total aggregate by
absolute volume
10 208 40
20 186 35
40 165 30
* Water content corresponding to saturated surface dry aggregate.
Note : This table is to be used for concrete grades up to M 35 and is based on following conditions
(1)Crushed (angular) coarse aggregate, confirming to IS 383-1 970.
(2)aggregate consisting of natural sand conforming to grading zone-II of table -4 of IS 383-1970;
(3) water-cement ratio of 0.6 (by mass).

(4) Workability corresponding to compacting factor of 0.80. (Slump 30 mm approx)
TABLE 6.5
APPROXIMATE SAND AND WATER CONTENTS PER CUBIC METRE OF CON CRETE FOR GRADES ABOVE M 35

wlc = 0.35, workability = 0.80 C.F.
Nominal
maximum size
– of aggregate (mm) Water content* per
cubic meter of concrete
(kg) Sand as percentage of
total aggregate by
absolute volume (%)
10 200 28
20 180 25

* Water content corresponding to saturated surface dry aggregate.
For other conditions of workability, water-cement ratio, grading of fine aggregate, and for rounded aggregates, certain adjustments in the quantity, of mixing water and fine to total aggregate ratio given in table 6.4 and 6.5 are to be made, according to table 6.6.

TABLE 6.6
ADJUSTMENT OF VALUES IN WATER CONTENT AND
SAND PERCENTAGE FOR OTHER CONDITIONS
Change in condition
stipulated for table 4.7
and 4.8
(1) Adjustment required in
Water
content
(2) Percent sand in total
aggregate
(3)
For sand confirming to grading
zones I, Ill or IV of table 4
of IS. 383-1970
(Standard zone is II) 0
+ 1.5 percent for zone .1
– 1.5 percent for zone III
– 3.0 percent for zone IV
Increase or decrease in value
of compacting factor by 0.1(Standard value = 0.80) ??3 percent 0
Each 0.05 increase or decrease in free water cement ratio. Standard value = 0.60) 0 ?? 1 percent
For rounded aggregate – 15 kg/m3 – 7 percent

Step-5 : Calculation of cement content
The cement content per unit volume of unit volume of concrete may be obtained from free water cement ratio obtained in step-2, and the quantity of water per u in step-4,.a’The cement content so obtained should be checked against the minimum cement content -2000)for the requirements of durability as per table 5.4 (table-5, IS 456 and the greater of the two Values adopted.

Step-6 : Calculation of Aggregate content:
With the quantities of water and cement per unit volume of concrete and the ratio of to total aggregate already determined, the total aggregate content per unit volume of concrete may be calculated from the following equations.

V = [W+(C/Sc)+(1/P)*(Fa/Sfa)]*(1/1000) for fine aggregate.

V = [W+(C/Sc)+(1/1-P)*(Ca/Sca)]*(1/1000) for Coarse aggregate.

Where,
V= absolute volume of fresh concrete, which is equal to the gross (m3) minus the volume of entrapped air.
W= Mass of water (kg) per m3 of concrete.
C= Mass of cement (kg) per m3 of concrete
Sc= Specific gravity of cement, say 3.15
P = Ratio of fine aggregate to total aggregate by absolute volume
Fa,Ca = Total masses of fine aggregate and coarse aggregate (kg) per concrete respectively.
Sfa, Sca = Specific gravities of saturated surface dry fine aggregate and
aggregate respectively Normally Sfa = 2.6 and Sca = 2.7 are used.

6.4 Experimental work:
Step-1 Target mean strength of concrete
Fck, = fck +t*s
= 25 N/mm2
t = 1.65from table 6.1 for proportion of low results 1 in 20
s = 4.0 from table 6.2, for M 25 grade of concrete.
Fck’ = 25+l.65*4
=31.6 N/mm2 (MPa)
Step-2 Selection of water-cement ratio
From fig. 6.1 the free water-cement ratio required for the target mean strength of 31.6 N/mm2 is 0.44.
Now, from table 5.4(table 5,pf IS : 456-2000), the maximum free water-cement ratio for ‘moderate exposure’ is 0.50. V
Hence, the free water-cement ratio is taken as the minimum of above two values i.e w/c=.44
Step-3 Estimation of air content
For maximum sie of aggregate of 20 mm, the air content is taken as 2.0%
(table 6.3).
Step-4 : Selection of water and sand content
From table 6.4, for 20 mm nominal maximum size aggregate and sand conforming to grading zone-11, water content per cubic meter of concrete = 186 kg and sand content as percentage of total aggregate by absolute volume = 35% i.e.
Water = 186 kg /m3 of concrete
Sand = 35% of total aggregate by absolute volume.

Change in condition
(Refer table 6.6) Adjustment required
Water content
% Percentage sand total aggregate
(i) For decrease in water-cement
ratio (0.60 – 0.44) that is 0.16 0 -3.2
(ii) For increase in compacting
factor (0.92 – 0.8) = 0.1 +3.6 0
(iii) For sand conforming to zone-I of table 4 of IS 383-1970. 0 +1.5

Total +3.6 -1.7

Required water content = 186 + (186*(3.6/100))
= 192.69 lit/m3
Required sand content as percentage of total aggregate by absolute volume
p =35-1.7
= 33.3%
Step-5 : Determination of cement content :
Water-cement ratio = 0.44 .
Water = 192.69 litre =192.69 kg
W/C=0.44
192.69/c=.44
C=437.93 kg/m3
this cement content is adequate for “moderate exposure” condition, according to table 5.4 (table-5, IS : 456-2000)

Step-6: Determination of fine and coarse aggregate content
Consider volume of concrete = 1 m3
but, entrapped air in wet concrete = 2%
Absolute volume of fresh concrete= 1-0.02=0.98m3
V=0.98m3.
For fine aggregate.
V = [W+(C/Sc)+(1/P)*(Fa/Sfa)]*(1/1000)
V=573 kg/m3
For Coarse aggregate.
V = [W+(C/Sc)+(1/1-P)*(Ca/Sca)]*(1/1000)
V=1255kg/m3
Step-7: Mix proportion(by mass)

Water Cement F.A. C.A.
191.69 lit 436 kg 563 kg . 1149 kg
0.44 1 1.34 2.88

Step-7 : Quantities for 1 bag of cement
Water Cement F.A. C.A.
191.69 lit 50 kg 64.5 kg . 132kg

7.1 INTRODUCTION:
It has been noticed that all super plasticizers are not showing the same extent of improvement in fluidity with all types of cements. Some super plasticizers may show higher fluidizing effect on some type of cement than other cement. There is nothing wrong with either the super plasticizer or that of cement. The fact is that they are just not compatible to show maximum fluidizing effect. Optimum fluidizing effect at lowest dosage is an economical consideration. Giving maximum fluidizing effect for a particular super plasticizer and a cements very complex involving many factors like composition of cement, fineness of cement etc.Although compatibility problem looks to be very complex, it could be more or less solved by simple rough and ready field method. Incidentally this simple field test shows also the optimum dose of the super plasticizer to the cement. Following methods could be adopted.
1. Marsh cone test.
2. Mini slump test
3. Flow table test.
Out of the above, Marsh cone test gives better results. In the Marsh cone test, cement slurry is made and its flow ability is found out. In concrete, really come to think of it, it is the aggregates, its shape and texture etc. will have some influence, it is the paste that will have greater influence. The presence of aggregate will make the test more complex and often erratic. Marsh cone is a conical brass vessel, which has a smooth aperture at the bottom of diameter 5 mm.The profile of the apparatus is shown in Fig 7.1.
7.2 PROCEDURE:
Take 2 kg cement, proposed to be used at the project. Take one liter of water (w/c = 0.5) and say 0.1% of plasticizer. Mix them thoroughly in a mechanical mixer (Hobart mixer is preferable) for two minutes. Hand mixing does not give consistent results because of unavoidable lump formation which blocks the aperture. If hand mixing is done, the slurry should be sieved through 1.18 sieves to exclude lumps. Take one liter slurry and pour it into marsh cone duly closing the aperture with finger. Start a stop watch and simultaneously remove the finger. Find out the time taken in seconds, for complete flow out of the slurry. The time in seconds is called the ‘Marsh Cone Time’. Repeat the test with different dosages of plasticizer. The dose at which the Marsh cone time is lowest is called the saturation point. The dose is the optimum dose for that brand of cement and plasticizer or super plasticizer for that w/c ratio.

PERMA PLAST

SANGHI OPC 53 AMBUJA PPC
DOSAGE (%) TIME (SEC) DOSAGE (%) TIME (SEC)
1.0 25.00 1.0 22.09
1.1 23.47 1.1 20.38
1.2 22.78 1.2 19.07
1.3 20.90 1.3 18.34
1.4 20.22 1.4 19.25
1.5 17.54 1.5 XXX
1.6 18.60 1.6 XXX
FIG 7.1 MARSH CONE FUNNEL
7.3 TEST RESULT:

8.1 Compressive strength test:

The compressive strength of grade M25 was studied on different ages of concrete, with different types of cement. This is the long term strength study, thus we have selected different age of concrete such as 7 days, 28 days for O.P.C and P.P.C Cement.
The concrete is mixed with the help of concrete mixer machine. Coarse aggregate, sand was first taken in to the mixer machine and mixed thoroughly. Then cement is add with required proportion, was taken in to the mixer machine with 60% water + plasticizer. Then mixer was started to revolve for the proper mixing. During this time only, the remaining 40% water + plasticizer were added in the mix. after proper mixing ,the concrete is placed in the cube moulds in three layers. Each layer was tamped 25 times with tamping rod and then vibrated for required time. The cube moulds were then placed on level surface for required setting of concrete. The concrete cubes are then numbered and placed for the moist curing. After 24 hours of casting, the next day all the cube moulds were opened and concrete cubes were placed for wet curing in the water tank.
The cubes were then tested on the required time period. Before testing, the set of cubes was surface dried in the air. all the cubes were tested on Digital Compression Testing Machine of capacity 2000KN compressive load. Total 24 cubes were casted for this test. The result of cube compressive strength of the cubes are presented as follows
ORDINARY PORTLAND CEMENT
Plain cement concrete Concrete with admixture.
7 days
(IN N/MM?? ) 28 days
( IN N/MM?? )
7 days
(IN N/MM?? ) 28 days
( IN N/MM?? )

21.42 32.83 29.33 35.72
20.83 33.58 27.26 38.55
23.75 31.72 31.85 36.97

Fig 8.11 (Splitting Tensile Strength Test: Cylinder with compression loading along the vertical diameter)
PORTLAND POZZOLANA CEMENT
Plain cement concrete Concrete with admixture.
7 days
(IN N/MM?? ) 28 days
( IN N/MM?? )
7 days
(IN N/MM?? ) 28 days
( IN N/MM?? )

20.11 28.37 27.13 29.35
19.33 29.52 23.67 30.38
21.25 30.31 26.52 32.56

‘

8.20 Tensile strength test for cylinder
It is the standard test, to determine the tensile strength of concrete in an indirect way. This test could be performed in accordance with IS 5816 : 1999.A standard test cylinder of concrete specimen (300 mm X 150mm diameter) is placed horizontally between the loading surfaces of Compression Testing Machine as shown in FIG. The compression load is applied diametrically and uniformly along the length of cylinder until the failure of the cylinder along the vertical diameter. To allow the uniform distribution of this applied load and to reduce the magnitude of the high compressive stresses near the points of application of this load, strips of plywood are placed between the specimen and loading platens of the testing machine. Concrete cylinders split into two halves along this vertical plane due to indirect tensile stress generated by Poisson’s effect. Due to this compressive loading, an element lying along the vertical diameter of the cylinder is subjected to a vertical compressive stress and a horizontal stress (Fig). The loading condition produces a high compressive stress immediately below the loading points. But the larger portion of cylinder, corresponding to its depth is subjected to uniform tensile stress acting horizontally. It is estimated that the compressive stress is acting for about 1/6 depth and the remaining 5/6 depth is subjected to tension due to Poisson’s effect.
Assuming concrete specimen behaves as an elastic body, a uniform lateral tensile stress of ft acting along the vertical plane causes the failure of the specimen, which can be calculated from the formula as,
Ft = 2P?? (??DL)
p = compressive load at failure.
L = Length of cylinder.
D = Diameter of cylinder.

Fig 8.12(Splitting Tensile Strength Test: Cylinder with compression loading along the vertical diameter)

The test result represents the “Splitting Tensile Strength” of concrete that varies between 1/8 to 1/12 of the cube compressive strength.
ORDINARY PORTLAND CEMENT

Plain cement concrete Concrete with admixture.
7 days
(IN N/MM?? ) 28 days
( IN N/MM?? )
7 days
(IN N/MM?? ) 28 days
( IN N/MM?? )

2.12 3.02 2.31 3.30
2.23 3.18 2.90 3.32
1.96 2.93 2.12 3.40

PORTLAND POZZOLANA CEMENT
Plain cement concrete Concrete with admixture.
7 days
(IN N/MM?? ) 28 days
( IN N/MM?? )
7 days
(IN N/MM?? ) 28 days
( IN N/MM?? )

2.04 2.94 2.18 3.07
2.14 2.64 2.30 3.14
1.91 2.76 1.94 2.75

8.30 Flexural strength test for beam:
After the Splitting tensile test another common test performed for determination of tensile strength is the Flexure test. The test could be performed in accordance with as per I.S. 516-1959, a simple plain concrete beam is loaded at one-third span points. Normal standard size of specimen is 150x150x750 mm. If the largest nominal size of the aggregate does not exceed 25mm, size of 150x150x500 mm may also be used. Span of the beam is three times its depth.

Fig 8.13 (Flexure Tensile Strength Test: Beam with two point loading at one-third of its span)
The typical arrangement for the test is shown in Fig-5 above. Equal Loads are applied at the distance of one-third from both of the beam supports. It induces equal reaction same as the loading at both of the supports. Loading on beam is increased in such a manner that rate of increase in stress in the bottom fiber lies within the range of 0.02 MPa & 0.10 MPa. The lower rate being for low strength concrete and the higher rate for high strength concrete. From the above loading configuration it is clear that at the middle one-third portion, in between two loadings, beam is subjected to pure bending. No shear force is induced
Within this portion. It is this portion of beam where maximum pure bending moment of Pd/2 is induced accompanied by zero shear force.
Fig8.14 (Flexure Tensile Strength Test: Beam with two point loading at one-third of its span)
As loading increases, if fracture occurs within the middle one-third of the beam, the maximum tensile stress reached called “modulus of rupture” fbt is computed from the standard flexure formula,
Fbt = pL ?? bd??
P = load at failure.
L =beam span between supports
d = Depth of beam.
B = width of beam.
Fbt = Modulus of rupture.
If fracture takes place outside the middle one third, then, according to I.S. 516-1959, the test result should be discarded.
ORDINARY PORTLAND CEMENT
Plain cement concrete Concrete with admixture.
28 days
( IN N/MM?? ) 28 days
( IN N/MM?? )

5.16 6.47
5.36 6.93
5.05 6.25

PORTLAND POZZOLANA CEMENT
Plain cement concrete Concrete with admixture.
28 days
( IN N/MM?? ) 28 days
( IN N/MM?? )

5.27 6.23
5.13 6.44
5.69 6.33

‘

Looking to the observation and test results obtained from this experimental work the following conclusion based on (1) Mix design, (2) Properties of hardened concrete with and without plasticizer (S.O.S).
9.1.1 Based on mix design
Strength of concrete developed systematically in following three stages: establishment of its specific properties, selection of ingredients and mix design.
Attempt has been made to produce high strength concrete with commonly used ingredients such as cement, sand and coarse aggregate, which are locally available.
9.2.2 Based on properties of hardened Concrete with and without admixture.
For the hardened concrete, its performance and life is decided on the characteristics of its properties such as Compressive strength, Tensile strength, Flexural strength etc.In this Project work all these properties were checked critically and conclude from the result obtained as follow:

 

From the project test result the compressive strength of concrete by adding admixture is generally 7 to 10 % higher than plain cement concrete for Ordinary Portland Cement and 10 to 15% higher for Portland pozzolana cement and also flexural strength of concrete by adding admixture is generally 26% higher than plain cement concrete for Ordinary Portland Cement and 18% higher for Portland pozzolana cement
‘ IS 383:1970 ‘ Specification for coarse and fine aggregates from natural sources for concrete
‘ IS 650:1991 Specification for standard sand f or testing of cement
‘ IS 2386(Part 1):1963 Methods of test f or aggregates f or concrete: Part 1 Particle size and shape
‘ IS 4031(Part 1):1996 Methods of physical tests for hydraulic cement: Part 1 Determination of fineness by dry sieving.
‘ IS 2386(Part 3):1963 Methods of test for aggregates f or concrete: Part 3 Specific gravity, density, voids, absorption and bulking.
‘ IS 10262:2009 Guidelines for concrete mix proportioning.
‘ IS 12269:1987 Specification f or 53 grading ordinary Portland cement.
‘ IS 650:1991 Specification for standard sand for testing of cement.
‘ IS 5513:1996 Specification for vicat apparatus.
‘ IS 7320:1974 Specification for concrete slump test apparatus.
‘ Concrete technology by M.S. SHETTY.