Properties of concrete in the plastic state
1. essential properties
The quality of hardened concrete largely depends on the quality of plastic concrete. The curing process also contributes to the realization of the specified design criteria. Since the consistency of the mixture can vary, careful adherence to the design criteria is of the utmost importance. When testing materials for suitability the only variable factor in a plastic mix may be the ratio, which must be precise. Plastic concrete must be workable, free from separation of coarse aggregates and of uniform quality.
The practicality of a plastic mix is the relative ease or difficulty of placing and compacting concrete. The consistency of the mixture must be maintained in order to achieve the practicality required for the specific conditions and method of placement. The deceleration test that is used to measure the consistency of a mixture is also a measure of workability. To perform this test, mixed concrete is placed in a standard cone in three respective layers, roughly equal in volume, and each layer is rode 25 times. The last layer is placed, rodded, and struck. The cone is then lifted vertically from the plastic concrete, which is allowed to collapse or solidify. The measurement of settlement below the top of the cone is recorded as a measure of the pliability of the mixture. The maximum or minimum deceleration shall be as per the specifications for the particular job. If a constant amount of material is used, the deceleration should remain constant. Any marked variation in deceleration or stability will immediately indicate a deviation from the mix design. An investigation should be done immediately to find out the cause.
3. no split
Plastic concrete should be handled and placed so that it is free from segregation of coarse aggregates and is completely homogeneous. To prevent separation, plastic concrete should not be dropped for a distance of more than 3 to 5 feet, or allowed to fall free.
For homogeneity of mixing, each batch should be in exact proportion as per the design criterion. Uniformity increases the economy of the mix and improves the quality of hardened concrete.
properties of concrete in the hardened state
1. essential properties
The essential properties of hardened concrete in pavement are similar flexural strength and durability.
Concrete pavements must have sufficient flexural strength to bear the required load. To obtain the desired strength, the most important factor is the ratio of water and cement. In general, no more than 7 gallons and less than 4 gallons of water are required for each sack of cement. Although a high water-cement ratio increases the yield of each sack of cement, a thinner paste is inherently weaker and the evaporation of excess water during the curing process leaves spaces that will reduce the strength of hardened concrete. .
The durability of finished concrete is the ability of artificial stone to resist the effects of weather, such as wind, frost, snow, ice action, and the combined effects of wet-drying and freezing-thawing cycles; chemical reaction of the soil or the effect of salts; and friction. Durability is affected by climate, pavement thickness and exposure. As the water-cement ratio increases above a minimum of 4 gallons per sack, durability is likely to decrease accordingly.