Material Testing

Cement we use may go bad during transportation and storage prior to its use in work.We need to test the cement for a good quality and better performance in concrete mixtures. Broadly there are two tests for cement-

• Field Testing
• Laboratory Testing

Field Testing
It is generally done when cement is used for small or minor works. Following are the field tests-

• After opening the bag of cement, we should give a good look, There should not be any visible lumps present in it. Colour of cement should be greenish grey.
• It should give a smooth and gritty feeling when pinch of cement is feel between the fingers.
• If we thrust our hand into the cement bag, it must give a cool feeling.There should not be any lumps inside.
• If we throw some amount of cement into a bucket of water, it should float sometime before sinking.
• A cube made from a stiff paste of 100gm cement and little water is to be put in a glass plate. The glass plate is taken slowly under water in a bucket. The shape of the cube should not be deformed while taking into water. After 24 hours cube should retain its original shape.

If a sample of cement truly satisfies the above tests we may say that the cement is not bad. But the above tests do not really indicate that the cement is really good for important work or big structure. For using cement in important and major structure, it should satisfy the Indian Standard specifications. It is possible only in laboratory testing to confirm the requirements of specified physical and chemical properties.
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By
KAUSHAL KISHORE
Materials Engineer, Roorkee

Most of our construction sites do not have field-testing laboratory. In this paper simple test methods of construction materials are described which could be performed without any machine or special equipments.

1. TEST FOR ORGANIC IMPURITIES IN FINE AGGREGATE
The aggregate must be checked for organic impurities such as decayed vegetations, humus, and coal dust, etc. Colour test is a reliable indicator of the presence of harmful organic matter in aggregates except in areas where there are deposits of lignite.

Procedure:
a) Fill a 350 ml clear glass medicine bottle upto 75 ml mark with a 3% solution of caustic soda or sodium hydroxide.
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The advantages of using Rowe cell over oedometer apparatus are:

(i) It possesses the control facilities for drainage and for the measurement of pore water pressure.

(ii) It is capable of testing larger diameter soil samples. Hence, more reliable data can be provided by using Rowe’s cell because of the relatively smaller effect of structural viscosity in larger specimens.

(iii) Rowe cell uses hydraulic loading system which is less susceptible to the effect of vibration than oedometer apparatus.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Particle density of soils is defined by the ratio of soil particle mass and soil particle volume. Depending on soil types, the range of variation of soil particle density varies not significantly, i.e. by 4%. Therefore, it may not be worthwhile to order laboratory tests and incur additional expenditure just to determine the particles density by recognizing that the variation of particles density is not significant.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

There are two major techniques of particle size distribution:

(i) Sieve analysis – for soil particles larger than 60?m they can be separated by this method.

(ii) Sedimentation analysis – for soil particles smaller than 60?m, they are too small to be sieved by sieve analysis. Instead, the particle size distribution is worked out from the rate of settlement of soil particles suspended in water by Stoke’s law.

In sedimentation analysis, the soil under testing is firstly boiled with little distilled water to wet and break up the particles. After that, hydrogen peroxide is added to remove any organic material. Then the whole mixture is allowed to stand still for a night and then boiled again to remove hydrogen peroxide.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Packer test is used in unlined drillholes in rock to test the permeability. In single packer test, the hole is drilled to the bottom of first test section and the top of the test section is sealed off by a packer. Water is then delivered to the test section and it is kept at constant pressure and the flow is measured.

In highly fractured rock there is a high chance that water tends to leak around the packer which gives inaccurate result. As such, multiple packers are adopted instead in which three sections of the drillhole are sealed up and water is pumped to them at equal pressure. This eliminates the tendency for water to flow around the packers from the middle section.

Hence, a more accurate result could be obtained by measuring flow from the middle section alone.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

INTRODUCTION
Concrete can be converted into precast masonry units such as Hollow and Solid normal and light weight concrete blocks of suitable size to be used for load and non-load bearing units for wallings. Use of such concrete blocks are more appropriate in region where soil bricks are costly, poor in strength and are not available. Depending upon the structural requirements of masonry unit, concrete mixes can be designed using ingredients available locally or if not found suitable then with in the most economical distance. The concrete mix used for normal hollow and solid blocks shall not be richer than one part by volume of cement to 6 parts by volume of combined room dry aggregates before mixing. Hollow concrete blocks for normal work used in masonry when reinforced is used shall not be leaner than 1 part cement to 8 parts room dry sand by volume. The mixes are designed with the available materials to give overall economy and the required properties of the products. The hollow load bearing concrete blocks of the standard size 400 x 200 x 200 mm will weight between 17 and 26 kg (1063 to 1625 kg/m3) when made with normal weight aggregates. Normal weight blocks are made with cement, sand, gravel, crushed stone and air-cooled slag. The grading for sand used in Hollow concrete block shall be as given below:
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By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

This method of test describes the procedures for determining concrete permeability to water by capillary absorption method for comparison between controlled specimens and the specimens containing admixtures having surface coatings. This method gives the waterproofing efficiency of admixtures and coating, thus also of the greatest interest for durability of concrete offers protection to reinforcement from corrosion.

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By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

Designers and builders of construction projects no longer can consider quality control testing an option or convenience. In the past decade, testing for the quality of materials and finished construction has become a necessity that no responsible builder can neglect.

The truth of this statement is proved not only by construction delays and cost overruns but also by catastrophic failures of major structures. Such catastrophies include dam failures, collapses and foundation breakdowns in multi-storeyed office and apartment structures; and other failures in stadia, factories, schools, auditoria, public buildings and bridges.

Each construction project determines its own individualized testing needs. A variety of factors influence the type of testing required. Among these factors are size of the structures, terrain, type of soil and subsurface conditions at the construction site and other conditions peculiar to the specific location. The expertise of the construction engineers and technical personnel working on the project will also have an influence on the testing and inspection need.
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Soil inspection or say geotechnical inspection is very important in understanding the physical properties of soil and the rocks beneath. This is required to ascertain the the type of foundation required for the proposed construction. Various tests are done to explore the sub surface and surface characteristics of soil .Some of these are given below.

Just click on the link to go to the details of that particular test

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