Various Shapes of River Gravels

They rolled tens of miles, some perhaps hundreds from the mountainous interiors to the flat plains through the help of rain, heat and water flows. Many had lived thousands of years, scoured from the bedrocks to become boulders, cobbles, and then gravels. The bedrocks in Sarawak are generally sedimentary in nature, which are easier to erode but the metamorphosed action and volcanic intrusion help to harden the rock which laid the basis for forming these hard gravels. Graywacke, sandstone, slate, phyllite, quartzite, limestone, etc. are common gravelly materials. There are many shapes and sizes too, round, oval, triangular, squarish,irregular, you name it, but most of them are smoothened and rounded at the corners. They are beautiful creatures formed by Nature.

Thirty years ago, these gravels were used for construction of concrete structures, especially in Sibu, where there was no igneous rock quarry but plentiful supply of river gravels. Concrete strengths were seldom expected to be more than Grade 30 (30 N per sq.mm). Actually, Grade 20 was most of the time adopted for design. Low strengths were due to the unpredictable strengths of gravels and often stained with a lot of silty materials. In fact, I also used the crushed boulders for some of the bridge foundation blocks in the Sarawak interiors. More cement was often required for such concrete.

Today, I collected these materials for landscaping.