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.
