Simple durability test for cement stabilized blocks

Compressed and cement-stabilized blocks are now recognized as important walling units for building low-cost dwellings in developing countries. Although the durability of their surfaces under in-service exposure conditions in the humid tropics has become a major matter of concern, it has received little formal research. Premature deterioration - as typified by surface erosion, mass loss, pitting, cracking and crazing - is common. A weather-resistant surface is required if a block is to remain durable for its service lifetime. However, current accelerated ageing tests to predict the overall performance of blocks under conditions causing surface deterioration (wetting, abrasion and drying) are inadequate. A new method is required that can be applied to blocks immediately after curing to evaluate the likely durability of their surfaces. The present paper explores the suitability of using the slake-durability test, originally developed for argillaceous rocks, to evaluate the durability of low-cost walling materials. During the test, surface erosion leading to mass loss of between 1 and 50% is recorded within only 10 minutes, representing an acceleration of in-service ageing by a factor of around 1 million. The test method proved reliable, controllable and repeatable. More importantly, the ranking of materials via their performance in this test correlated well with a ranking of their durability in service based on long professional field experience in Uganda. It is concluded that the slake-durability test not only is robust, but also provides a quick predictive surface and quality test for cement-stabilized blocks and other like materials.