Pozzolanic characterization of waste newspaper ash as a supplementary cementing material of concrete cylinders

The landfill disposal of waste newspapers has triggered an environmental concern that must be addressed. The ink from the waste newspaper is toxic and could be leached out of the waste newspapers by rainwater at landfill sites, causing water contamination. This contributed to the degradation of aquatic ecosystems. In another environmental problem, cement manufacturing resulted in a large emission of carbon dioxide into the air. Considering all these issues, it is necessary to investigate waste newspaper ash as a supplementary cementing material in concrete cylinders for cleaner production. The waste newspaper ash was produced by incineration in an electric furnace at 800 C for 1 h before it was cooled down and sieved. Based on the ACI 211.1-91 standard, two sets of concrete cylinders were cast, namely control and waste newspaper ash treated concrete cylinders; each having a size of 150 mm diameter 300 mm height. They were cured in water for 3 to 90 days before being tested for their mechanical and chemical properties. The mix design of 7.5% waste newspaper ash as partial cement replacement in the treated concrete cylinders was found to be the optimal one. The optimally treated concrete cylinder was tested to have an average 28-day compressive strength of 33.28 MPa, which is 2.15 MPa lower than the control ones. At 90-day curing age, however, its average compressive strength value was traced to be 44.06 MPa, which is 3.17 MPa higher than the control ones. Investigation of the surface morphology and X-ray diffraction patterns of the treated concrete cylinder samples revealed that there was a progressive pore refinement and a continuous decrease in portlandite when the curing age was prolonged from 28 to 90 days. Inspection of a failed 90-day optimally treated concrete cylinder revealed that it had higher stiffness and fewer extreme macrocracks compared to that cured in 28 days. These positive outcomes pointed out that the pozzolanic reaction in the optimally treated concrete cylinders was pronounced at 90-day curing age and added to their strength improvement in the long term.