Testing of Concrete Blocks

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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Simple Testing Of Admixtures And Surface Coating For Permeability To Water.

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.

For all test specimens materials, proportions, workability, mixing, compaction, casting, curing, temperature and testing method should be kept identical for conclusive comparison between controlled and admixture/coated specimens.

Casting of Specimens
10cm cubes of the following mix are to be cast by hand compaction filling the cubes in two layers each layer to be rammed 35 times by ramming rod 16mm dia 600mm in length one end bullet pointed. A set of 3 cubes shall be prepared with the recommended dosage of admixture. The other set of 3 cubes shall be made without any admixture (controlled cube). In case of surface coating is to be tested, then all the six cubes shall be made of the same mix.

Mix Proportions
OP Cement 43 grade = 200 Kg/m3
Sand Zone II = 850Kg/m3
20-5mm aggregate = 1115lg/m3
Water= To give slump of 40+-5mm or compaction factor of about 0.90.

The above is a suggested mix of sand and aggregate having specific gravity of 2.6. Mixes may be designed as per local aggregates.
Cement:Aggregate ratio should be kept 1:9 to 1:10

Liquid admixtures usually reduce the water demand, but in very lean mixes there shall not be much reduction in mixing water.
The water of the liquid admixture should be accounted in the mixing water. A few trials of controlled concrete workability will be required for getting the exact quantity of mixing water for obtaining required workability. As far as possible this controlled concrete mixing water should not be exceeded with the admixture mix. The lean mix as recommended above will be desirable for this type of test.

Procedure of Testing
After 24 hours of casting, all the cubes shall be demoulded and cured in clean water in the same curing tank for 28 days. After 28 days of curing all the cubes shall be dried in a ventilated oven at the temperature of 100oC to +-10oC till constant weight. If surface coating is to be tested, then as per recommendations of the manufacturer three cubes to be surface coated at one face and upto the height of 5 cm on all the four faces. After coating and conditioning, these cubes along with the controlled cubes shall again be died in the oven at a temperature of 50oC to +-2oC till constant weight. Coated cubes faces should be kept upward while keeping them in oven, sot that coating should not be damaged. The coating after its application should withstand without any physical and chemical change a temperature of 50oC, which is a temperature normally reached of concrete surfaces exposed to sun at most places of India during summer. A coating sensitive to this temperature should not be tested with this method.

All the six weighted cubes shall be placed in the same glazed or glass flat tray, so that the cubes are dipped up to a level of 1.2cm. The level of the water shall be maintained throughout the experiment by adding fresh water from time to time. Evaporation of water from exposed cubes surfaces and tray is prevented by covering the entire set up by polythene. Care should be taken that polythene should not disturb the set up. Determine the gain in weight of the cube at different intervals till the weight of cube become constant.

The permeability of each cube of a set shall be found by determining the coefficient of water absorption with the help of the formula:

A= Mw/t
Where A – Coefficient of water absorption.
Mw – Amount of water absorbed per unit area.
T – Time in second for absorption

From the test results the effectiveness of admixtures and coating may be compared with controlled specimens. This method is simple for testing waterproofing admixtures and coating without any special equipment.

This paper by Er. Kaushal Kishore was first published in NBM&CW magazine.

Setting Up Small Testing Laboratory at Field

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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Various Lab Test On Soil

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
1) Water Content – There are two test which can be done to determine the water content of soil. These are
a) Calcium Carbide Method
b) Oven Drying Method
Other tests on soil are :
2) Free Swell Index Of Soil
3) Plastic Limit Of Soil
4) Liquid Limit Of Soil
5) Particle Size Distribution Of Soil
6) The Specific Gravity Of Soil
7) The In-Situ Dry Density Of Soil By Sand Replacement Method
8 ) The In-Situ Dry Density Of Soil By Core Cutter Method
9) The Maximum Dry Density And The Optimum Moisture Content Of Soil

Apart from these some Soil Compaction Tests are also done. See this for details

Various Lab Test On Bitumen

Bitumen is a mixture of organic liquids that is black, highly viscous, sticky product used for paving roads, waterproofing products (used in sealing roofs). There are many tests which are conducted to check the quality of bitumen. Bitumen is very important component of many construction sites like roads, highways. Many tests are done to ensure the quality of bitumen. Some of these are given below :-

1. Bitumen Content
2. Ductility Of Bitumen
3. Penetration of Bitumen
4. Specific Gravity of Bitumen
5. Softening Point Of Bitumen
6. Flash And Fire Point Of Bitumen
7. The Marshall Stability of Bituminous Mixture

Just click on the names of the tests above to know the entire procedure of how we perform these tests.

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