Visual Inspection of Concrete Structure

Kaushal Kishore
Materials Engineer, Roorkee

Visual inspection is one of the most versatile and powerful of the NDT methods, and it is typically one of the first steps in the evaluation of a concrete structure. Visual inspection can provide a wealth of information that may lead to positive identification of the cause of observed distress. However, its effectiveness depends on the knowledge and experience of the investigator. Broad knowledge in structural engineering, concrete materials, and construction methods is needed to extract the most information from visual inspection.

Before performing a detailed visual inspection, the investigator should develop and follow a definite plan to maximize the quality of the record data. Visual inspection has the obvious limitation that only visible surface can be inspected. Internal defects go unnoticed and no quantitative information is obtained about the properties of the concrete. For these reasons, a visual inspection is usually supplemented by one or more of the other NDT methods, such as by concrete test hammer, ultrasonic concrete tester and partial destructive testing by drilling cores and testing them for compressive strength.
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Properties Of Green Lightweight Aggregate Concrete

Ali Shokati Sayyad, MS Student Of Islamic Azad University Chaloos Branch Kooros
Nekoofar Asisatant Professor Of Islamic Azad University Chaloos Branch

With increasing concern over the excessive exploitation of natural aggregates, synthetic lightweight aggregate produced from environmental waste is a viable new source of structural aggregate material. The uses of structural grade lightweight concrete reduce considerably the self-load of a structure and permit larger precast units to be handled. In this paper, the mechanical properties of a structural grade lightweight aggregate made with fly ash and clay will be presented. The findings indicated that water absorption of the green aggregate is large but the crushing strength of the resulting concrete can be high. The 28-day cube compressive strength of the resulting lightweight aggregate concrete with density of 1590 kg/m3 and respective strength of 34 MPa. Experience of utilizing the green lightweight aggregate concrete in prefabrication of concrete elements is also discussed.
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Polymer-Modified Mortars And Concrete Mix Design

Kaushal Kishore
Materials Engineer, Roorkee

Polymer-modified Concrete (PMC) has also been called polymer-Portland cement-concrete (PPCC) and latex-modified concrete (LMC). It is defined as Portland cement and aggregate combined at the time of mixing with organic polymers that are dispersed or redispersed in water. This dispersion is called latex; the organic polymer is a substance composed of thousands of simple molecules combined into large molecules. The simple molecules are known as monomers, and the reaction that combine them is called polymerization. The polymer may be a homopolymer if it is made by the polymerization of one monomer, or a copolymer when two or more monomers are polymerized.

Of various polymer-modified mortar and concrete, latex-modified mortar and concrete have superior properties, such as high tensile and flexural strength, excellent adhesion, high waterproofness, high abrasion resistance and good chemical resistance, to ordinary cement mortar and concrete. Accordingly they are widely used in many specialized applications in which ordinary cement mortar and concrete have been employed to a lesser extent till now. In these applications, the latex-modified mortars are widely used rather than the latex-modified concrete from the viewpoint of a balance between their performance and cost.
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Quality Control Of Construction Testing Of Concrete Cubes

By Kaushal Kishore
Materials Engineer, Roorkee

The acceptance criteria of quality of concrete is laid down in IS:456-2000. The criteria is mandatory and various provisions of the code have to be complied before the quality of concrete is accepted. In all the cases, the 28-days compressive strength shall alone be the criterion for acceptance or rejection of the concrete. In order to get a relatively quicker idea of the quality of concrete, optional test for 7 days compressive strength of concrete be carried out.

6 Cubes of 150 x 150 x 150 mm size (the nominal size of aggregate does not exceed 38 mm) shall be cast, 3 for 7-days testing and 3 for 28-days testing. A set of
3 cubes (specimen) average strength will be a sample. The individual variation of a set of 3 cubes should not be more than ± 15% of the average. If more, the test result of the sample is invalid.

Note:- For aggregates larger than 38 mm, bigger than 150 mm moulds are to be used. See IS:10086-1982
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Development Of Light Weight Concrete

Dhawal Desai
IIT Bombay

This paper deals with the development of two types of lightweight concrete the one using lightweight aggregate (Pumice stone) and the other water floating type using Aluminium powder as an air entraining agent. This also shows the importance of water/cement ratio as in first type of concrete it relates to the smoothness of the surface and in second one it is a major factor which controls the expansion of concrete.

Lightweight concrete can be defined as a type of concrete which includes an expanding agent in it that increases the volume of the mixture while reducing the dead weight. It is lighter than the conventional concrete with a dry density of 300 kg/m3 up to 1840 kg/m3. The main specialties of lightweight concrete are its low density and low thermal conductivity.
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