Investigation into volcanic ash and calcium hydroxide as a building block binder

Abstract

The emerging rise of carbon emissions in the environment is a global challenge due to negative impacts like global warming. A considerable amount of these carbon emissions originates from the manufacture of Portland Cement. The production of one tone of Portland Cement generates one tone of carbon dioxide. In addition to this, the manufacture of cement is expensive. There is an increase in the demand of cement in the construction industry as a result of increased population. This implies that there is need to develop a more sustainable alternative binder to cement to facilitate the construction industry in an environmentally friendly way. This research focused on investigating an alternative binder using volcanic ash mixed with calcium hydroxide for building blocks hence completely eliminating cement as a building block binder. VA is a low cost natural pozzolan that can be accessed from unexploited deposits in Uganda and CH is available as lime from the market. VA and CH react together in the presence of water to form complex compounds with cementitious properties required to form the binder in building blocks. The VA was obtained from Rubanda district and calcium hydroxide was obtained from Cheap hardware store in Kasubi. The VA and CH obtained were characterized by carrying out pH, Loss on Ignition and X-Ray Fluorescence tests on them. The volcanic ash was then prepared by grinding until all the particles were finer than 80 microns. Proportions of volcanic ash to calcium hydroxide of 90:10, 80:20, and 75:25 (percentage by mass) were mixed in the laboratory to make three different binders by basic design of experiments using factorial testing. The properties (setting time, standard consistency and compressive strength) of these binders were investigated. The binder of a VA:CH ratio of 80:20 gave the highest compressive strength and it was used to make solid blocks using a binder to stone dust ratio of 1:6 by volume with a water to cement ratio of about 0.5. These blocks were tested for compressive strength at 3, 7, 21 days. The strength at 28 days was obtained by extrapolation using equations 3.1 and 3.2 of clause 3.1 in BS EN 1992-1-22004. Water absorption was tested at 7 and 21 days. These results were compared with those obtained from a control experiment done using blocks made out of Pozzolanic Portland Cement (CEM IV B, 32.5). The blocks made out of the new binder passed the water absorption requirement. This implies that these blocks are not susceptible to significant moisture attack. The blocks met the standard minimum compressive strength of concrete blocks used for walling of 2.8MPa according to Standard Specifications for Building Works by MOWT (2013), Part 1 Section 5, table 1-9. The blocks can also find application in low-cost housing for walls that support only their own self-weight