A study on use of recycled demolition debris in construction

The particle size distribution of output material is affected by type of crusher used .The demolition debris of particle size less than 37.5 mm. The inclusion of upto 15% of particle larger than 37.5 mm should not alter density significantly. Water absorption of coarse and fine particle of crushed brick aggregates passing 19 mm 4.75 mm respectively and retaining on 4.75 mm are 6.15 % and 6.20 %(coarse) and 6.87 % and 7.16% (fine) for the samples from site 1 and site 2 respectively. Material passing the 0.425 are non plastic. The 0.075mm sieve were limited to a maximum of 2% although this percentage was permitted to rise to10% if the fines of this size were non plastic. It was observed that crushed concrete had 10% fine values of 145kN and 67-97kN for demolition debris but other material have values greater than 50kN . The crushed masonry appeared to be weakest materials. The specific gravity of limestone was 2.55 compared with 2.63 and 2.34 for crushed concrete and demolition debris respectively. The water absorption value were 0.50% for limestone,9.32 for demolition debris and 3.76% for crushed concrete. The high value for demolition debris was attributed to the porosity of the mortar and brick in the material. The demolition debris has dry density of 81.7% . This lower density was partly due to the difference in specific gravity of the material. Particle density of crushed brick aggregates passing 19 mm and retaining on 4.75 mm are 2.67 t/m and 2.65 t/m for the samples from site 1 and site 2 respectively. Generally a higher density was obtained on site than in laboratory at a moisture content lower than the laboratory optimum which suggest that site compaction was more effective . It has observed that the moisture content of a fine grained soil is increased, the dry density(d) also increase until it reaches at a point of peak density(dpeak). Maximum density of crushed brick samples under modified compactive effort are 2.02 t/m and 1.96 t/m. Limestone and crushed concrete showed high CBR values in the range of 250% to 500%. A CBR value greater than 100% can only be interpreted as meaning that the material had a greater bearing capacity than crushed rocks. The standard force for 2.5 mm and 5mm penetration are 13.24kN and 19.96kN respectively and CBR is calculated for both levels of penetration. The critical state direct shear angle of friction (ds)cv tend to 42 when estimated from the exploration. The dense sample showed an early peak in the shear strength but the loose sample achieved maximum shear strength. The crushed concrete had a slightly higher (ds) value at 50kN/m and than (ds) decrease as v increased.