Division of Natural Sciences and Mathematics

The curing temperature and time are the basic fundamental factors that contribute to the hydration of Ordinary Portland Cement (OPC) paste. The purpose of this work is to investigate the effect of temperature vis-à-vis curing time on the hydration products: Portlandite (CH), calcium silicate hydrate (C-S-H), ettringite (AFt) and monosulfoaluminate (AFm) of Japan OPC paste using the water-cement ratio (w/c) of 0.40 and following intensive procedures in sample preparation and testing. Results showed that the proportion of CH and C-S-H phases dominated the hydration products at higher curing temperature and longer time as revealed in BEI/SEM analysis. The XRD/Rietveld analysis showed that the CH had the highest peaks intensity compared to other crystalline phases cured at 40 o C for 28 days. It has a mineralogical composition equivalent to 20.06% compared to 17.80% as OPC cured at room temperature. There was no C-S-H phase detected since it is non-crystalline/amorphous in nature with composition equivalent to 61.75%. The conversion of AFt to AFm phase from 0.12% to 3.10% was also detected at higher curing temperature and longer time. The CH is the major crystalline phase identified in this study.

Mullite from clay is well studied but there has been no report on the Solsona White Clay-alumina
(SWC-Al2O3) substitution in the mullite compositions. The synthetic mullite obtained from this work is
the product of the synthesis of the beneficiated Solsona white clay (SWC) sourced from Ilocos Norte,
Philippines; Alumina (Al2O3) powder reagent from J.T. Baker Inc., USA; and Siruma silica (SiO2) from
Bicol, Philippines.
The formulation was based on the theoretical composition of mullite that is 71.79% Al2O3 and 28.21%
SiO2; modified with a proportional substitution Al2O3 to the SWC by 5%, 10%, 15%, 20%, and 50% and
kept the SiO2 constant. The five formulations were processed separately and then characterized using
SEM, XRD and EDX.
Formulation with 5%, 10% and 15% SWC revealed the presence of pores, formation of column-like
grains, acicular and small islands of a locally textured grainy structure when sintered at 1150°C for 7hrs;
and the formation of nodular grains when sintered at 1400°C for 7hrs. While formulations with 20% and
50% SWC demonstrates with preferred grain alignment and huge grain growth after sintering at 1150°C
for 7hrs and further transformed into a nucleated particle and amorphous/glassy phase when sintered at
1400°C for 7hrs.