Comparative study of established test methods for aggregate strength and durability of Archean rocks from Botswana

ABSTRACT Comparative study of established test methods for aggregate strength and durabilityof Archean rocks from Botswana In the current situation, river sand is used for building of roads and as raw material forconcrete in Botswana. River sand is a finite resource and important to preserve as itacts as natural water purification, groundwater aquifer and protection against soil erosion.Mining of bedrock may be a good alternative to replace the river sand with crushed rock(aggregates) in concrete and as road materials.The main purpose of this thesis was to determine if the rock grain size can be usedas a parameter to indicate durability and rock strength. It was also of interest to find outif the grain size correlates with established technical analysis and strength test methods.This knowledge can be used as a prospecting tool when searching for new quarry sites inthe future.In this master’s thesis, rock samples from the Gaborone granite complex have beenanalysed to examine how established test methods and the mineral grain size correspondswith the rock strength. By comparing technical properties (Los Angeles (LA) value ,aggregate crushing value (ACV), aggregate impact value (AIV) and 10 percent fines aggregatecrushing test (10 % FACT)) with quantitative analysis (mineral grain size andmineral grain size distribution), it is possible to determine the mineral grain size correspondenceto rock strength. Generally the result show that more fine-grained granitesshow better technical properties than more coarse-grained granites. The calculated meangrain size show weak negative correlation to ACV value, and a positive correlation to LA-, AIV- and 10 % FACT values. Best correlation can be seen between mean grain size andLA values (R2= 0.61) and AIV values (R2= 0.58). Low mean grain size tend to give bettertechnical properties in form of lower LA- and AIV values. The cumulative distributioncurve show that a high concentration of very fine material or fine material tend to contributeto a lower LA value. The results indicate that equigranular rocks with low meangrain size contributes to good technical properties, but when it comes to uneven grainedrock more factors must be taken into account to estimate technical properties