An investigation into the productivity of block laying on building sites in Kampala
Ouga, Allan Dickens
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On many public buildings, use is made of concrete blocks. Previous research shows that the productivity of workers is a major cause of poor performance of building projects in Uganda. As such poor productivity of block laying could result in cost overruns, delays and claims. However, there has been no detailed study to document productivity of block layers in terms of work output in comparison with individual attributes of block layers. This is important for proper scheduling of numbers of helpers and other resource planning during construction. This study therefore investigated the productivity of block layers on building sites in Kampala. Data were collected from 160 block layers from 40 building sites in Kampala. In addition, data were collected from individual block layers, site engineers, contractors, clerks-of-works, and building developers on socio-economic factors that influence productivity amongst block layers using a questionnaire. Data were analysed by use of Statistical Package for Social Scientists (SPSS), Microsoft Excel and RStudio. The results show that productivity of block layers is significantly influenced by; work height, number of porters assigned to a block layer and a statistical interaction between the level of education and experience of a block layer. The results further show that the most frequently used blocks in Kampala are of sizes; 400x150x200mm and 400x225x200mm. It was established that at the plinth and with 400x225x200mm blocks, the average productivity of a block layer is 1.15 square meters per hour. The highest productivity recorded with the 225mm thick blocks is 1.18 square meters per hour attained at a wall height interval of (0-1) m while the least is 0.7square meters per hour attained at (5-6) m height interval. For 400x150x200mm blocks, the highest productivity of 1.37sq.m/ hour was obtained at a height interval of (0-1) m and 0.88sq.m/ hr being the least productivity obtained at a height interval of (5-6) m from the ground level. It was concluded that the sizes of concrete blocks commonly used in Kampala differ from the those specified by the Ugandan Ministry of Works and Transport (MoWT). Block laying productivity drops with increase in wall height and block size. It however, rises with a combination of skill and experience levels of a block layer. Increase in the number of porters assigned increases the block laying productivity up to a certain point where an extra porter causes productivity to reduce. Other factors that influence block laying productivity include; late supply of materials and equipment mismanagement, disruption of supplies such as water. The model developed is statistically significant at 95% confidence level, and predicts 65% of the variability in block laying productivity. From the study results, it is recommended that in order to enhance productivity of block laying, block layers should attain relevant skills/experience through vocational studies. Bidders/contractors for block work should rely on acceptable benchmarks to build rates for block work. The current study should be extended in the future to address key issues that would improve predictive ability of the current model for which there was no sufficient researched data. There is need to explore the effect of outside environment(working under sunshine), mortar-mixing and transportation technologies, block laying tools and wages on productivity of a block layer.