Megamix places high priority on the quality control aspect of our products. We apply stringent monitoring right from the sourcing of raw materials, to all stages of our production process as well as the final testing procedure, to ensure that all our products are in compliance to B.S. 5328 standard or as specified by the project specification.
Quality assurance based on test certificate issued by cement manufacturer, comply with M.S. 522.
Fine and Coarse Aggragate
Quality of fine and coarse aggregate are tested in the procedure covering the following elements :
– sampling of fine and coarse aggregate
– main sample for fine and coarse aggregate
– sample reduction for fine aggregate – Quartering Method
– sample reduction for coarse aggregate – Rifle Box Method
– sieve analysis for fine and coarse aggregate
– moisture content of fine aggregate
– determination of clay, silt and dust in fine aggregate
1. Sampling of fine and coarse aggregate
The following apparatus is used :
– A scoop of width not less that four time the maximum particle size of the material.
– Dust proof containers / baskets.
– A rifle box for reducing sample.
2. Main sample for fine and coarse aggregate
2.1 The main sample is obtained by collecting in the dust-proof container / basket at least 10 portion or increment by means of the scoop.
2.2 The portions are taken from different areas of the bulk, quantity in such a way a represent, as far as possible, the average quality.
2.3 The portions taken should add up to weight not less than that give in Table 1 (MS522).
|TYPE OF MATERIAL||NOMINAL SIZE||MINIMUM WEIGHT OF SAMPLE (KG)|
|Coarse Aggregate||Smaller than 25.4mm and larger than 4.76mm||25|
|Fine Aggregate||4.76mm or smaller||13
3. Sample reduction for fine aggregate – Quartering Method
3.1 The main sample is dampened, if necessary with clean tap water.
3.2 The main sample is thoroughly mixed and heaped into a cone and then turned over to form a new cone.
3.3 This carried out three times and each conical heap is formed by depositing each shovelful of the material on the apex of the cone so that the potions which slide down the sides are distributed as evenly as possible.
3.4 The third cone is flattened and divided into quarters.
3.5 One pair of diagonally opposite quarters is discarded and the remainder forms the sample for testing.
3.6 If the sample is still too large, it can be reduced by further quartering.
4. Sample reduction for coarse aggregate – Rifle Box Method
4.1 The main sample is discharged into Rifle Box and two halves are collected into two boxes at the bottom of the chutes on each side.
4.2 One half is discarded and rifling of the other half is reported until the sample is reduced to the desired size.
5. Sieve analysis for fine and coarse aggregate
To carry out the Sieve Analysis the following apparatus shall be used :
Test sieve – 200mm diameter. Scale accurate to 0.5% of the mass of test sample.
5.1 The sample size for sieve analysis of 2 kg for coarse aggregate and 0.2 kg for fine aggregate.
5.2 The samples are air dried and weighed prior to sieving.
5.3 The sieve sizes for coarse aggregate are 37.5mm, 20mm, 10mm and 5mm.
5.4 The sieve sizes for fine aggregate are 10mm, 5mm, 2.36mm, 1.18mm, 0.6mm, 0.3mm and 0.15mm.
5.5 Shake the sieve containers for a minimum of two minutes.
5.6 The aggregate retained in each sieve shall be weighed.
5.7 The percentage passing is determined and plotted on the sieve analysis graph.
5.8 The grading of coarse aggregate and sand shall be within the limits specified in table 1 and 2 respectively.
Table 1 – Grading For Coarse Aggregate
|BS 410 Test Sieve||% Passing By Weight
|20mm Single Size|
|20.0mm||90 – 100%||85 – 100%|
|10.0mm||30 – 60%||0 – 2%|
|5.0mm||0 – 10%||0 – 5%|
Table 2 – Grading For Fine Aggregate
|BS 410 Test Sieve||% Passing By Weight
|5.0mm||89 – 100%|
|2.36mm||60 – 100%|
|1.18mm||30 – 100%|
|600mm||15 – 100%|
|320mm||5 – 70%|
|150mm||0 – 15%|
6. Moisture content of fine aggregate
The Apparatus required for the carrying out of the moisture content test is a Speedy Moisture Tester.
6.1 The sample is weighed on the balance/scales provided and then placed into a pressure cell.
6.2 Place a reagent to the other part of the cell.
6.3 Shake the cell and record the reading given by the pressure gauge.
7. Determination of clay, silt and dust in fine aggregate
The apparatus required for carrying out the determination of clay, silt and dust is a 250 measuring cylinder.
7.1 A 1% solution of salt water is prepared by adding 1 teaspoonful of common salt to 500ml of water.
7.2 Place 50ml of the salt water in the measuring cylinder.
7.3 Add the test sample gradually until the volume of the sample is about 100ml.
7.4 Add more salt water until the volume reach 150ml.
7.5 Shake the mixture vigorously until clay particles have been dispersed.
7.6 Place the cylinder on a level bench and gently tap the cylinder until the surface of the sand is level. Leave the cylinder standing for three hours.
7.7 After three hours record the height of the silt visible above the sand layer. Expressed this height as percentage of the height of the sand below.
Quality records are identified as :
|Sieve Analysis for Coarse Aggregate|
|Sieve Analysis for Fine Aggregate|
|Clay, Silt and Dust Content in Fine Aggregate|
|Moisture Content in Fine Aggregate|
|Field Assistant Report|
Quality assurance based on analysis report issued by manufacturer, comply with B.S. 5075.
JBA water supply, comply with B.S. 3148.
We would ensure that our standard design mix or any project specified proposed mix design have the desired workability and compressive strength prior to their incorporation into the permanent works.
Procedure of Trial Mix
1 Trial mix shall be carried out for each grade upon receipt of consultant approval.
2 Trial mix shall be carried out either by laboratory trial or production trial. On laboratory trial – proposed volume per batch = 0.04m³ and on production trial – proposed volume per batch = 2.00m³.
3 The operator shall set the weight for each constituent material in accordance to the mix design based on the volume required to be batched.
4 Trial mix report would be submitted.
TESTING OF CONCRETE
Cube Test Making
The following apparatus are required :
a. Cube mould (with a nominal size of 150mm x 150mm x 150mm).
b. Compacting bar.
1 Assembly the cube mould at a surface which is flat.
2 Filled the mould with three layers of concrete which each layers is approximately one third of the height of the mould.
3 Compact each layer with compaction bar. Distribute the strokes of the compaction bar in a uniform manner over the cross section of the mould.
4 Ensure that the compaction bar does not penetrate significantly any previous layer.
5 The number of strokes per layer required to produce full compaction will depend upon the workability of the concrete but in no case shall the concrete be subjected to less than 35 strokes per layer for 150mm cubes.
The following apparatus is used :
a. Wheel Barrow.
b. Tamping Rod.
c. Measuring Tape.
d. Slump Cone.
e. Slump Plate (Sampling Tray).
1 Hold the mould firmly against the surface below with the slump cone in position at the top whilst it is filled in three layers.
2 Each layer is approximately one third of the height of the cone when tampered.
3 Tamp each layer with 25 strokes of the tamping rod and the strokes being distributed uniformly over the cross section of the layer.
4 After the top layer has been tamped, remove the cone from the concrete by raising it vertically, slowly and carefully in 5s to 10s.
5 Measure the slump to the nearest 5mm by using the measuring tape to determine the difference between the height of the cone and of the highest point of the specimen being tested.
Test Cube Monitoring
1 Concrete cube is made at the site and details on the numbers of concrete cubes, structure, grade were recorded in the field assistant report.
2 The Quality Control Supervisor will refer to the field assistant report and will instruct the Field Assistant to dismantle the concrete cubes.
3 The concrete cubes is then cure in curing tank.
4 Details of the field assistant report is transfer to the concrete test log book.
5 When the concrete cube which is mature on the 7 days and 28 days, it shall be taken out of the curing tank and tested for compression strength.
Concrete Test Cube results would be recorded and compiled for statistical analysis when necessary.