Sandcrete blocks and bricks are masonry units manufactured from a mixture of cement, sand and water, and it plays a crucial role in the building construction. Sandcrete blocks are largely used for load bearing and non-load bearing walls and foundations.
Production process and necessary tests performed on both raw materials and sandcrete blocks are discussed in the following sections.
The manufacturing process of sandcrete blocks is as follows:
Measuring materials for sandcrete block production is called batching. There are two methods for batching including weight and volume method.
Fig. 1: Weigh batcher used to measure amounts of each materials
2. Mixing Materials
Mixing materials is carried out after batching. It could be done either manually or mechanically. The former method used for the production of large number of sandcrete blocks. However, the latter is advised when small number of blocks are needed.
Cement and sand shall be blended sufficiently and then water is added to the mixture. This process shall be done properly otherwise the block quality will be compromised.
Lastly, the addition of excessive water shall be prevented since it leads to shrinkage and distortion of the blocks on drying.
3. Molding Sandcrete Blocks
After mixing, molds will be filled with materials. Different machines and molds are available for use in the production of sandcrete blocks. For example, electric vibrating machine, hand press machine, and local steel/wooden hand mold.
The quality of blocks produced by each molding machine is different due to variations in the degree of compaction. The electric vibrating machine produces high quality and strength blocks compared with other moulding methods.
Fig. 2: Manual molding of sandcrete block
Fig. 3: Machine molding of sandcrete block
After molds are filled, the material is compacted to eliminate voids inside the mixed materials. Not only does the compaction process improve sandcrete block quality but also its durability. The compacted blocks are then pushed out of the moulds onto a flat surface.
Fig. 4: Removing block from the mold
5. Curing Sandcrete Blocks
It includes wetting of blocks with water so as to permit proper hydration and hardening to take place and eventually achieve full strength.
The application may be done by watering can, rubber hose or buckets, or sprinkling water on the blocks and covering with a tarpaulin or damp sacks.
Fig. 5: Curing sandcrete block
This is the arrangement of the blocks one on top of the other, ready for sale or use.
Fig. 6: Stacked blocks
Tests on Sandcrete Constituent
Fine Aggregates Testing
Sand used for sandcrete block production shall be clean and free from deleterious materials. Therefore, it is required to conduct tests on samples to ensure the suitability of the sand prior to its utilization.
1. Sieve Analysis
Sieve analysis may be performed based on Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates (ASTM C136 / C136M – 14) or any other applicable standards. It shows the suitability of sand for sandcrete blocks.
For example, if quantity of fine materials are high, then it is highly possible that block strength would be compromised.
2. Silt and Clay Content Test
This test can be conducted based on Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis (ASTM D7928 – 17) and IS : 2386 ( Part II) 1963.
3. Organic Content Test
Organic content test can be performed based on Standard Test Methods for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils (ASTM D2974 – 14)
Testing of Sandcrete Blocks
1. Compressive Strength Test
This test is used to evaluate compressive strength of sandcrete block. Compression strength is the ability of blocks to resist an axially applied load on the edge or the bed face of the block.
Compression testing machine is employed to evaluate the compressive strength of blocks. The test is conducted on blocks at 28 days of age and three samples are tested. The load is exerted on the block till it crushes; at this point maximum compressive load will be recorded.
2. Bulk Density
This test begins by labeling and numbering samples. Then, weigh each sample in dry states and record their masses. The dimensions (the length, breadth and height) of each block is taken from which volume of samples are computed. Finally, the bulk densities are calculated using the results.
3. Water Absorption
Water absorption test on sandcrete block include weighing samples in air, then fully immersed them in water for 24 hours. After that, the wet samples are taken out and weighed.
These values will be used to compute water absorption capacity which is expressed as a percentage. Water absorption is equal to the block wet weight minus dry weight divided by volume of block multiply by 100.