The effect of rice husk ash as pozzolan in addition to cement Portland class G for oil well cementing

•Rice husk ash as pozzolan in addition to or partially replacing well cement slurry.•Chemical reactivity and features of rice husk ash for use in oil well cementing.•The hot water washing treatment (WRHA) afforded higher reactive silica than RHA.•The well cement slurry WRHA20 presents a reduction of 72.75% of calcium hydroxide.•The well cement slurry WRHA20 increases 63.69% at compressive strength.

The usage of rice husk biomass ash from agribusiness in addition to or partially replacing cement is a noble purpose and a good way of sustainable development which currently is an obsession around the world. Although rice husk contains high amount of organic material, it has less percentage of inorganic material which is rich in silica and used for this paper purpose. In this study the pozzolanic material was obtained from two different processes: by calcining (RHA) and by washing with hot water (WRHA). The ash samples were characterized by: scanning electron microscopy technique (SEM), Fourier transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX) and BET method. The pozzolanic activity of RHA and WRHA in cement slurries was evaluated by thermal-gravimetric technique and derivative thermogravimetry (TGA/DTG), X-ray diffraction (XRD) and Compressive Strength. The slurries formulated with additions of 10% and 20% of RHA and WRHA were cured for 28 days at 58 °C. The results of thermal analysis demonstrated that a 20% WRHA addition caused a reduction of approximately 73% of Portlandite (calcium hydroxide – CH) phase related to standard slurry (STD). The XRD scans also demonstrated the reduction of the Portlandite peaks׳ intensity for each slurry compared with STD slurry. The RHA and WRHA react chemically with Portlandite producing calcium silicate hydrate (C-S-H), confirming their effect as a pozzolanic agent. The WRHA presented the best results as a pozzolanic material.