Month: January 2023

Here a rod is embedded in concrete blocks. These are pulled out and the strength of the concrete is determined. The ideal way to use the Pullout test in the field is to incorporate assemblies for pull out in the structure itself. These could be pulled out and the strength determined.

Here X-rays and gamma rays are used. When X-rays and gamma rays are passed through concrete, the electromagnetic spectrum penetrates concrete but undergoes attenuation in the process. The degree of attenuation is a function of the kind of matter traversed, its thickness and the wavelength of the radiation. Further, the intensity of the incident gamma-rays… Continue reading Radioactive Method

This is a new technique which is used to determine the moisture content and the cement content. This method employs the scattering of neutrons directed towards the concrete and the number of neutrons returned. With a standard relationship number of neutron and water content/cement content, the required water or cement content can be obtained.

It is another important non-destructive method used to determine the compressive strength and other properties. The fundamental principle on which the method is based is the velocity of material through a material. A mathematical relation could be made between the resonant frequency of the material to the Modulus of Elasticity of the material. The property… Continue reading Frequency Method

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