Category: Concrete

This is a commonly adopted equipment for measuring surface hardness. It consists of a spring control hammer which slides on a plunger and is housed in a tube. Once the plunger is pressed against the surface of the concrete, the mass behind the spring rebounds. After impact, the spring control mass rebounds and takes the… Continue reading Schmidt’s Rebound Hammer

Non-destructive testing is done on hardened concrete. In non-destructive testing methods, some properties of concrete are used to estimate strength, durability, elastic parameters, crack depth, micro-cracks and progressive deterioration of concrete. Such properties of concrete are hardness, resistance to penetration of projectiles, rebound number, resonant frequency, ability to allow ultrasonic pulse velocity, ability to scatter… Continue reading NON-DESTRUCTIVE TESTING

Quality control implies that the assigned work is done according to the specifications agreed in the contract. Major civil engineering works such as multistoreyed buildings, dams, harbours, etc., have to be constructed with utmost care as they have to last and be used for decades. Specifications of work should be framed based on cost or… Continue reading QUALITY CONTROL OF CONCRETE

Improper formwork with less rigidity may lead to sinking, bending, etc., and the wet concrete may cause cracks or deformation after compaction which may go unnoticed.

During the initial stages of curing, uninterrupted hydration is a must. Due to the hot sun, winds and lower relative humidity, young concrete dries faster leading to plastic shrinkage cracks.

Water being light in weight moves upward in concrete, which leads to bleeding. This water evaporates to make the top surface porous having very little abrasion resistance. Masons often float the concrete when the bleeding water is still standing on the surface. Too much of working on the exposed surface leads to pressing the coarse… Continue reading Cracks Due to Bleeding

Plastic concrete settles when vibrated. There will be no cracks if the concrete settles uniformly. Some cracks are bound to occur if there is any obstruction to uniform settlement due to reinforcement or larger pieces of aggregates. Such cracks are called settlement cracks. Such cracks are formed generally in deep beams.

Evaporation of water from fresh concrete is due to the absorption by formwork and during the hydration process. The surface of concrete dries up when the loss of water from the surface of the concrete is faster than the migration of water from the interior to the surface. This creates a moisture gradient which results… Continue reading Plastic Shrinkage Cracks

Factors that contribute to the formation of cracks in cement concrete are discussed below.

The following tests are commonly employed to measure workability of fresh concrete: Slump Test It is the most commonly used method of measuring consistency of concrete. This test can be conducted in the field or in a laboratory. However, this test is not suitable for very wet or very dry concrete. The apparatus for conducting… Continue reading Testing of Fresh Concrete