Influence of additives & CO2 injection on practical properties of excelsior cement boards

In order to examine the effect of additives and as well the injection of CO2 on excelsior cement boards, excelsior produced from poplar (Poplus sp) and the Portland cement type 2, and two additives, CaCl2 (calcium chloride) and Al2(So4)3 (aluminum sulfate) with 3% & 5% concentrations was used. The results showed that the board containing 5% of CaCl2 have better mechanical properties that may be attributed to effective neutralization of inhibitory agents of cement originated from wood and better cement hydration. CO2 injection in mat prior the pressing had negative effect on the board properties which is considered as consequence of chemical reaction between cement and CO2, significant increase in hydration temperature in this stage and presetting of cement before press that result in improper cement bonding. Analyzing physical & mechanical properties of produced boards showed that excelsior-cement boards treated with CaCl2 have acceptable properties and higher bending strength and internal bonding as compared to ordinary excelsior-cement board. Therefore appropriate condition to manufacture these boards is the application of CaCl2 5% as an additive without CO2 injection before pressing the excelsior-cement cake.