Carbonation of Concrete Carbonation of concrete is one of the reasons for corrosion of reinforcement. It is a process by which carbon dioxide from air penetrates into the concrete and reacts with calcium hydroxide to form calcium carbonates. The percentage of CO2 present is air vary from place to place. In case of rural areas … Read more
Points to Consider Mixing of mineral admixtures with OPC at site should not normally be permitted. However for projects requiring use of blended cement from durability and strength considerations, which is not available from the cement manufacturer blending may be permitted through a specific facility created at site with complete automated process control to achieve … Read more
The following 4 mineral admixtures can be used for making concrete. Rice husk ash Metakaolin Silica fume Fly as 1. Rice Husk Ash It is obtained by burning the rice husk in a controlled manner without causing environmental pollution. This is generated in huge quantity in the rice shelters and each tone of paddy produce … Read more
Factors Affecting Strength Test Results of Concrete Compressive strength is the most important property of concrete. The compressive strength of concrete is determined in the laboratory in controlled conditions. On the basis of this test result we judge the quality of concrete. But sometimes the strength test results vary so widely that it becomes difficult … Read more
Generally we specify workability of concrete in terms of its slump test value. But sometimes it is also specified by another test called compaction factor. The relation between slump and compaction factor is roughly as follows. Relation Between Slump & Compaction factor Workability Slump in mm Compaction factor Very stiff – 0.70 Stiff 0 to … Read more
Properties of Cement Concrete The cement concrete possesses the following important properties: It possesses a high compressive strength. It is a corrosion resistance material and atmospheric agent has no appreciable effect on it. It hardens with age the process of hardening continues for a long time after the concrete has attained sufficient strength. It is … Read more
The following properties of aggregate affect the properties of hardened concrete. 1. Grading Aggregate grading has no significant effect on the properties of hardened concrete. 2. Bulk Density This has no direct effect but has an indirect effect on drying shrinkage. Bulk density is an indicator of packing capacity, which influences water requirement, which in … Read more
The followings are general recommendations or considerations for hot weather concreting. Guidelines to Follow 1. Do not exceed the maximum allowable water-cementious materials ratio or the manufacturer’s maximum recommended dosage of any admixture. 2. Consider retarding admixtures if their performance has been verified during trial batches. 3. Substitute ground, granulated blast furnace slag for part … Read more
Bleeding cannot be completely prevented as it is an inherent property of concrete. But it can be minimized if following precautions are taken. By proper proportioning of concrete mix. By mixing the concrete uniformly and completely. By using finely divided pozzolanic materials ( as it creates a longer path for the water to traverse and … Read more
What is Laitance? Laitance is caused by bleeding of concrete. In case of bleeding, only water accumulates at the top of the surface, but in case of laitance, along with water certain quantity of cement also comes to the surface, forming a thin layer of cement paste at the surface. This formation of cement paste … Read more