Opportunities for improved sustainability in house building: The case of Dar es Salaam

The combination of a growing population and economic development in Africa will form strong drivers for building growth. Buildings drive energy consumption and carbon emissions. On the material side, cement is the driver for cost and carbon emissions. A cement productivity index is proposed. Results from a case study in Dar es Salaam show that cement is poorly used in the main application of sandcrete blocks. The relative cement productivity is < 30% compared to ordinary concrete. The main problem is the design of the blocks. Mostly, only some 5% of cement by weight is used. However, the sand matrix often needs up to 10% of water for good compaction. This means that the w/c ratio is always high in the mixes, which leads to low cement productivity. One first step could be going from solid to hollow blocks, which would enable increasing the cement content and improving cement productivity up to 50% of the defined benchmark. However, there is resistance to hollow blocks in the market. Alternative solutions, such as soil-stabilized earth, should also be looked into. For realizing the full cement strength potential, other affordable concrete solutions need to be developed for the market.