A to Z of cement
Aggregate give body to the concrete, reduce shrinkage and effect economy. They merely occupied 70-80 percent space in concrete volumes. Concrete have two phases; paste phase and aggregate phase.
When ordinary cement clinker ground or blended with suitable proportions of GGBS or natural or artificial pozzolans. Pozzolan is a siliceous or siliceous and aluminous material that it self-possesses little or no cemetitious value but will, in finely divided form and in the presence of moisture, chemically react with the calcium hydroxide at ordinary temperature to form compounds having cementitious properties. Calcium hydroxide is produced in ordinary cement along with cementitious compound and responsible for disintegration of concrete in long duration.
Cement is a binding material produced by intimately mixing together calcareous material like limestone and argillaceous material like clay and silica. Cement is second most usable material after water for the construction of concrete world-wide.
Curing means keeping the concrete moist and warm enough so that the hydration of cement can continue. Water is the most usable material for the curing of the concrete after lying.
Dry process is the cement manufacturing process which is widely used all around the world. Raw material grind very fine and proportionally mixed and processes in kiln to form clinker. The process is quite economical to earlier used wet process.
Density of the cement is 1440 Kg/cum
The cement used for the grouting purpose which used to defeat the cement property of shrinkage to fill the space tightly.
Elasticity of concrete refer as “Modulus of elasticity (Ec) and is equals to root of Fck.Fck is the characteristic compressive strength of concrete.
The time elapsed between the moment the water added to cement and the time when cement paste completely lost the plasticity. As per Indian Standard final setting time will not be more than 600 minutes.
Fly ash is the finely divided residue that results from the combustion of ground or powered coal and that is transported by flue gasses. Fly ash act as a pozzolan and used as additive in PPC cement. As per Indian standard; fly ash addition range between 15 to 35 percent of total cementitious material.
False set is the rapid development of rigidity in fresh concrete, mixed paste, mortar without evolution much of heat and regain it plasticity by remixing is known as false set. When cement get permanently harden just after adding of water with high evolution of heat is known as Flash set.
An important bearing on the rate of hydration and hence on the rate of gain of strength and also rate of evolution of heat. Higher the fineness; higher the rate of gain of strength. Much higher fineness also leads to cracking in concrete.
Gypsum is added to cement to increase is setting time to make it useful product. Generally amount of gypsum varies in between 3 to 7 percent depend upon the material. Chemical composition of gypsum is CaSo4 2H2O.
The reaction between cement and water is known as hydration of cement. The reaction is exothermic in nature. C3S and C2S are the most important ingredients of the cement which contribute in strength development. During the hydration CSH gel start forming and paste gained the strength.
The time elapsed between the moment water is added to cement, to the time paste starts losing the plasticity of cement. As per Indian Standard, initial setting time will not be less than 30 minutes.
A expansion joint is catered in the long dimension concrete structure to counter the effect of dry shrinkage of concrete. Without these joints; crack will be developed. These type of joints play significant role in pavement concrete where length of concrete laid is very large.
The process of fusion of raw material takes place in rotary kiln to form clinker. The temperature of rotary kiln is 1450 C for the fusion.
Lime is the calcareous materials and used as a basic raw material for the cement manufacturing. Lime contains CaO which is 60 to 67 percent portion in raw material of cement.
lime saturation is the chemical element of cement and can be set lower or higher depending on the specification and cement requirement. Lower LSF means lower C3S and higher LSF means higher free lime content in the cement. The normal LSF value range in between for OPC clinker is 0.88 to 0.96.
It is a chemical element of cement and indicates the pre-hydration and carbonation effect on the cement. The pre-hydration may have resulted from the moisture introduced or absorbed during manufacture and storage. Generally the LOI is the indicator for the freshness of cement and it should not be more than 5 percent.
It is a chemical element of cement and generally found in raw material of cement. In clinker MgO act as a fluxing agent and therefore, in a small percentage it has a beneficial effect on clinker chemistry and the process of clinkerisation. Magnesia should not be more than 6 percent.
MTC means manufacturer’s test certificate. Cement manufacturer has to maintain a record of the properties of cement produced. Showing these properties, the cement manufacturer generally issued a certificate called MTC. If requested by consumer than manufacturer has to present or provide the MTC.
NDT means “ Non destructive Test” this method is for evaluating the concrete for its strength and durability. In the NDT method, the specimen are not loaded to failure and as such the strength inferred or estimated can-not be expected to yield absolute value of strength.
Ordinary Portland cementis the pure form of cement initially manufactured. OPC is currently classified into 43 and 53 grade cement.
Pozzolan is a siliceous or siliceous and aluminous material that it self-possesses little or no cemetitious value but will, in finely divided form and in the presence of moisture, chemically react with the calcium hydroxide at ordinary temperature to form compounds having cementitious properties. Few example of pozzolan are Fly ash, GGBS, silica fumes etc.
This type of concrete sets initially after about 5 minutes and sets finally in about 30 minutes. It is uses are generally restricted to works in running water and the repairs of roads that cannot be stopped for more hours. Concrete made with this type of cement should be kept moist after harden.
As name indicates it develop the strength rapidly and such it may be more appropriate to call it high early strength cement. Fineness and C3S are on higher side to achieve the maximum strength in initial period. Preferable use of rapid hardening cement in construction pre-fabricated structures, road repairs and cold weather concreting.
Specific gravity represents the relative weight of cement. The specific gravity of cement is obtained by using Le-chatelier flask. Generally, specific gravity of cement is around 3.15.
It is a zone between cement paste and aggregate. The binding property of cement is related to strong bond at transition zone. Higher w/c ratio, bleeding leads to weak transition zone.
Cement is considered when they cause unacceptable extend of the volume change in hardened concrete or mortar which causes crack and affect durability. Excess free lime and excess presence of MgO will create unsoundness in cement. Unsoundness reduces the durability of the structure.
This is the used method for the batching of concrete in India. It is not a very good method to batch the concrete because it is very difficult to accommodate the density and moisture in the concrete. Cement is always measured by weight then it is more appropriate to use weigh batching for the concrete ingredients.
Most important factor in concrete to control the properties. Strength of concrete is only dependent upon water cement ratio provided the mix is workable. Even the w/c ratio also controls the durability of the mix. Lesser the w/c higher the strength of concrete vice versa. The minimum amount of water required for the hydration of cement is 38 percent by weight of cement.
It is new method for the analysing of the hydraulic cement. It help in effectiveness of manufacturing process control, reduced the product variability and time taken for the complete analysis.
Yield is the volume of fresh concrete produced in a batch, expressed in cubic meters. It is calculated by dividing the total mass of the material by measured density of the fresh mixed concrete.
To evaluate the compatibility of admixture with concrete; zero slump concrete play a very important role to check the efficiency to increase the workability.