Abstract:
The macadamia shells have considerable high water absorption content and this is not desirable in concrete. But looking at it when the concrete has been cast and it is now left to hydrate the macadamia will absorb a lot of moisture which can be of use to hydrate the cement paste further in absence of moisture. The density of concrete with macadamia shells is much less compared to the normal concrete. The lower density is advantageous as it reduces the dead load of the structure. This makes the structure lighter. The compressive strength of the macadamia shells in concrete was observed to reduce with percentage increase hence the substitution was viable up to a certain percentage may be 30%. The strength was not so bad for the 10% replacement giving a value of 22.16N/mm2 for the 28days test which is 11% reduction from the normal concrete. Crushed macadamia shells have a high aggregate crushing value but the test was adjusted in the force used because of the high strains compared to the stresses required. The macadamia shells increase workability with increase in % replacement. However, the water/ cement ratio was observed that it needs to be adjusted slightly to carter for the water absorption and also to increase fluidity of the concrete. The 50% replacement showed that with the 0.55 w/c the concrete was too dry and the cement paste was not enough to make the aggregates interlock and hence the concrete was too porous.
Results from the effect of temperature tests showed that macadamia shells concrete has a high temperature resistance relative to normal concrete, however macadamia shells concrete is highly permeable due to its porous nature. At 50% replacement with macadamia shells the concrete was observed to be porous. The higher the porosity of concrete the better the insulation. This means that the insulation of concrete is improved with the higher percentage replacement.
