Use these IS codes to enhance the quality practices and the supply chain of aggregate
Aggregates are one of the key ingredients of concrete. They are cheap and abundant. Aggregates help enhance the strength and bonding of concrete. But how to select quality aggregates?
Refer to IS code.
The Bureau of Indian Standards publishes codes like these for the harmonious development of the activities of standardization, marking, and quality certification of goods. These codes are prepared after extensive research done across the country by reputed construction companies and organizations. The IS codes are freely available in public resources and can be downloaded from the internet. The BIS publishes the Indian Standard codes for the harmonious development…
Here are three important IS codes that can be your handy guide while selecting and using aggregate in construction.
IS 383: 2016 - Specification for coarse and fine aggregates for concrete (second revision)
This code covers the requirements of artificial and naturally available aggregates.
The code distinguishes aggregates into three types:
- Fine Aggregate
- Coarse Aggregate
- All-in Aggregate: Mix of coarse and fine
Here are a few key highlights from the code:
With the scarcity of naturally available aggregate, the code emphasizes the use of crushed aggregates. However, it also puts a limit on the usage of such aggregates due to functional limitations.
For example, The code does not recommend the usage of manufactured aggregate in pre-stressed concrete. Also, Table 1 of this code highlights the limits to the usage of manufactured aggregates.
Manufactured aggregates are further scrutinized with additional limitations, as given in table 3, 4, 5, 6 of IS 383: 2016
The IS codes are formatted in such a way that each clause contains a key takeaway for the practitioner. For example, clause 5 is about the quality of aggregates. In this, the code covers the limit of deleterious materials. You can refer to Table 2 for a detailed breakdown.
As you know, flaky and elongated aggregates make a non-cohesive mixture. So, their proportion should be limited. The code suggests the determination of these values for which you need to refer IS 2386 - part 1.
While sourcing the aggregates, one must also look for the mechanical properties to ensure the strength and durability requirement of the aggregates. The code suggests the following tests:
- Aggregate crushing value
- Aggregate impact value
- Aggregate abrasion value
The IS codes are prepared by considering the climatic condition of the Indian peninsula. Therefore, the code needs to consider every type of weather condition prevailing within the region. For example, in the northern parts of India, where snowfall is prevalent, the aggregate might get exposed to frost. To withstand these natural forces, the code suggests that the material should pass the magnesium or sodium accelerated soundness test as specified in IS 2386 -part 5.
Also, think of coastal and mountainous regions where high moisture content exists. Here, while concreting, the aggregate containing alkali might damage the concrete therefore, the code suggests tests (chemical method, mortar bar method, concrete prism test) be carried out which are described in the IS 2386 part 7.
Another challenge in concrete mix design is the size of an aggregate. If the structure has densely spaced reinforcement, then large-size aggregates won't work. The concrete thus will remain porous and weak. The concrete mix demands well-graded aggregates. The code, therefore, points out the size and grading of aggregates.
Finally, the code highlights on methods of sampling and testing of aggregate, which covers tests to be carried out while the batch of aggregate arrives on the site.
The code also speaks on
- Supplier's certificate and costs of tests
- Delivery terms
- Marking and standardization
Annexure A provides a list of aggregates from other than natural sources.
- Iron slag aggregate
- Steel slag aggregate
- Copper slag as aggregate
- Construction and demolition waste
Annex B contains details of information to be provided by the supplier - a useful guide for anyone dealing with aggregate business.
Annex C: Description and physical characteristics of aggregates from natural sources
Annex D: Determination of iron unsoundness for slag aggregates
Annex E: Determination of volumetric expansion ratio of slag aggregates
The Aggregate Supply Chain
Aggregates are usually sourced from natural rocks.
In the case of mega construction projects, the availability of aggregates in the nearby areas considerably saves the cost. Suppose there is a construction project to be carried out, or a city to be built. What is the process that will justify that the rock is suitable for use as aggregate? Is the available quantity sufficient?
After surveying the area, the potential rock quarry needs to be validated using sample tests. In such case, IS 2430:1986 - Methods for sampling of aggregates of concrete provide guidelines.
This code prescribes the methods of sampling for coarse and fine aggregates for the following purposes:
- Preliminary investigation of the source of supply,
- Investigation of shipment of materials
- Investigation of materials on the site of work.
This standard also mentions methods of sample reduction, packing, and dispatching them for examination and testing.
Let's say the quarry is sanctioned. Blasting is done. The aggregates are crushed, loaded, and transported. Next?
Once the aggregates arrive at the site, the challenge is to check the suitability and quality of the received aggregate. For that, one needs to carry out various quality tests. What are those tests that a quality engineer should carry out? What is the procedure for these tests?
Well, IS 2386: 1963 covers the method of testing for aggregates of concrete.
This code is divided into 8 parts. Here is the structure:
Part 1 covers particle size and shape
This section contains the following tests
- Sieve analysis
- Determination of materials finer than 75 microns
- Determination of flakiness index
- Determination of elongation index
- Determination of angularity number
Part 2 covers the estimation of deleterious materials and organic impurities
- Determination of clay lumps,
- Determination of clay, fine silt, and fine dust ( sedimentation method )
- Determination of light-weight pieces ( coal and lignite ),
- Determination of soft particles, and
- Estimation of organic impurities
Part 3 covers specific gravity, density, voids, absorption, and bulking
Determination of the following:
- Specific gravity and water absorption
- Bulk density and voids
- Necessary adjustment for bulking of fine aggregate (field method),
- Surface moisture in fine aggregate (field method )
Part 4 covers mechanical properties
- Determination of Aggregate Crushing value,
- Determination of the 10 percent Fines Value,
- Determination of Aggregate Impact Value,
- Determination of Aggregate Abrasion Value,
- Determination of the Polished Stone Value, and
- Determination of Crushing Strength.
Part 5 is about the soundness
Covers the method of test to determine the resistance to the disintegration of aggregates by saturated solutions of sodium sulfate or magnesium sulfate.
Part 6 is about measuring mortar-making properties of fine aggregates
The process includes a compression test on specimens made from a mortar of a plastic consistency and gauged to a definite water-cement ratio.
Part 7 is about alkali aggregate reactivity
Covers two methods of test for determining the potential reactivity of aggregates:
Part 8 contains details for petrographic examination
Covers methods of petrographic examination of aggregates for concrete.
In this article, you get a complete picture of the aggregates from sourcing to testing. Now you got an idea of how the aggregate supply chain works smoothly to maintain the quality standards of aggregates. But what about you? How do you maintain quality control on your site?
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