River Gravels

These gravels appear to be better aggregates for making concrete compared to the powdery limestone aggregates. It took hundreds or even thousands of years to grind the big rocks to these small gravels. But in Sarawak, most of the streams and rivers pass though sedimentary rocks and therefore these gravels are mainly of Sandstone, Mudstone, Siltstone and Limestone origins. The rocks are not hard enough to withstand heavy pressure. The aggregates are not suitable to make high strength concrete. But they are commonly used in rural regions for making low strength concrete not exceeding 25N/sq.mm. Most of the old buildings used the river gravels when quarried aggregates were not available. But the new building codes are getting stringent that some of the gravels may not be able to pass certain aggregate tests.