Study on applicability of ACI and DOE mix design methods for paving blocks

Abstract

Presently local manufacturers select the initial mix proportions for CPBs in a random basis and improve it through several trials to attain the final mix. Whereas either identification of new mix proportioning method or modification of existing mix design methods yet remains to be researched. In view of the above, applicability of contemporary mix design methods such as American Concrete Institute (ACI) Method and Department of Environment (DoE) Method to mix proportion the concrete paving blocks (CPBs) were studied experimentally in the present study. In line with both mix design methods, constituents of CPBs were estimated for characteristic compressive strengths, from 15 N/mm2 to 50 N/mm2, a range that approximately satisfies the requirements of the Sri Lankan Standard for CPBs. Based on the estimated proportions, trial mixes were cast and tested for compression at 7 and 28 days and from the experimental observations, some suggestions are made in this thesis. Moreover, adoptability of ACI mix design method with local materials is experimentally verified with limited number of test samples and it can be concluded that many sand samples being tested failed to fall within the fineness modulus range specified in ACI method, leaving local sand to be unsuitable in many cases. Hence, a method of combining sand samples is identified in the literatures and presented in the thesis, using which sand samples can be made suitable for ACI Method of mix proportioning. Further, effect of fine aggregate proportions on compressive strength was studied through set of experiments. Mix proportions were estimated using DoE method for Grade 15 and Grade 50 for finer and coarser sands (94% and 34 % passes through 600 μm sieves respectively) and cubes were cast. They were tested on 7 and 28 days and the test results have shown that the cubes cast with fine sand have attained slightly higher compressive strength to that of coarser sand.