Concrete Engineering

By
Kaushal Kishore
Materials Engineer, Roorkee

Cement concrete in India on large scale is being used since the last about 70 years. In the early days the following nominal ratio by volume for concrete were specified.

IS : 456-2000 has recommended that minimum grade of concrete shall be not less than M-20 in reinforced concrete work. Design mix concrete is preferred to nominal mix. If design mix concrete cannot be used for any reason on the work for grades of M-20 or lower, nominal mixes may be used with the permission of engineer-in-charge, which however is likely to involve a higher cement content.
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By
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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By
Ali Shokati Sayyad, MS Student Of Islamic Azad University Chaloos Branch Kooros
Nekoofar Asisatant Professor Of Islamic Azad University Chaloos Branch

Abstract
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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By
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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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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By
Dhawal Desai
IIT Bombay

ABSTRACT
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.

INTRODUCTION:
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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By
Dhawal Desai

ABSTRACT
This paper describes the effect of size of aggregates and proportions of cement, aggregates, admixture and water on porosity of Pervious concrete which is the main feature of pervious concrete. Different sample blocks were made in lab with variations in mixture to see the porosity for final conclusion

INTRODUCTION
Pervious concrete is a type of concrete with high porosity. It is used for concrete flatwork applications that allow water to pass directly through it, thereby reducing the runoff from a site and allowing groundwater recharge. The high porosity is attained by a highly interconnected void content. Typically pervious concrete has water to cementitious materials ratio (w/cm) of 0.28 to 0.40 with a void content of 18 to 35%.
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By
Kishor Sambhaji Sable (Faculty, Civil Engineering Department, Amrutvahini College of Engineering, Sangamner, Ahmednagar, Maharashtra, India)

Mehetre Amol Jagganath (Faculty, Civil Engineering Department, Amrutvahini College of Engineering, Sangamner, Ahmednagar, Maharashtra, India)

Abstract:
In this modern age, civil engineering constructions have their own structural and durability requirements. Fiber Reinforced Concrete (FRC) is a composite material made primarily from hydraulic cements, aggregates and discrete reinforcing fibers. Fiber incorporation in concrete, mortar and cement paste enhances many of the engineering properties of these materials such as fracture toughness, flexural strength, resistance to fatigue, impact, thermal shock and spalling.

The SFRC is a composite material made of cement, fine and coarse aggregates and discontinuous discrete steel fibers. Recently developed an analytical model to predict the shear, torsional strength and bending torsion behavior of fiber reinforced concrete beam with experimental substantiation. However, very little work has been reported in combined torsion and shear. Similarly to beam with conversional reinforcement, the presence of shear may significance influence on torsional strength of fiber concrete beams. Present paper investigates the mechanical properties like as shear strength, and torsion strength of concrete with different types of steel fiber with constant volume fractions and different aspect ratio.

Key words: Aspect ratio, Fatigue, Flexural strength, Fracture toughness, Mechanical properties, Spalling, Volume fraction.
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By
Kaushal kishore
Materials Engineer, Roorkee

The scarcity and availability at reasonable rates of sand and aggregate are now giving anxiety to the construction industry. Over years, deforestation and extraction of natural aggregates from river beds, lakes and other water bodies have resulted in huge environmental problems. Erosion of the existing topography usually results in flooding and landslides. Moreover, the filtration of rain water achieved by deposits of natural sand is being lost, thereby causing contamination of water reserves used for human consumption. Hence, to prevent pollution authorities are imposing more and more stringent restrictions on the extraction of natural aggregates and its crushing. The best way to overcome this problem is to find alternate aggregates for construction in place of conventional natural aggregates. Rubber aggregates from discarded tyre rubber in sizes 20-10 mm, 10-4.75 mm and 4.75 mm down can be partially replaced natural aggregates in cement concrete construction.

About one crore 10 lakhs all types of new vehicles are added each year to the Indian roads. The increase of about three crores discarded tyres each year pose a potential threat to the environment. New tyre is made of natural rubber (also called virgin rubber), styrene-Butadien Rubber (SBR), Polybutadienc Rubber (PBR), Carbon black, Nylon tyre cord, rubber chemicals, steel tyre card and Butyl rubber.
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By
Kaushal Kishore
Materials Engineer
Roorkee

INTRODUCTION:
SCREENERS companies near Dehradun and elsewhere have set up highly sophisticated as well as, eco-friendly screening and washing plants for the production of uncrushed (Shingle) coarse aggregates and coarse sand direct from river bed. These plants are producing and supplying uncrushed (Shingle) aggregates of sizes 40 mm, 20 mm, 12.5 mm and river coarse sand, which complies to the specifications of
IS : 383-19702.

Our construction sites, particularly Govt. Departments hesitates in the use of uncrushed coarse aggregate as so far they are being supplied to them direct from river bed or by manual sieving without washing them with water. Thus neither they are clean nor properly graded. This draw back is not with the uncrushed aggregates produces and supplied from SCREENERS modern plants with regular quality control. In this booklet the readers will find that when quality uncrushed aggregates are available not only economically but locally, our construction sites particularly Govt. Departments should not hesitate in the use of uncrushed aggregates from the river bed and save our environment, as crusher generate pollution. Further in all the Civil Engineering Codes uncrushed aggregates from river bed has been specified to be used in our all Civil Engineering Construction.
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