Strength and toughness improvement of cement binders using expandable thermoplastic microspheres

The effect of Expandable Thermoplastic Microspheres (ETM) loading on the fracture resistance and indirect tensile strength of cement binders is studied. Portland white cement (PWC) was used as the matrix in the current study. Loadings of 0.1%, 0.35%, 0.5%, 0.75% and 1%, by weight, of ETM were added to the dry cement. Semi-circular bend specimens, 152 mm in diameter and 27 mm thickness with different notch depths were fabricated to study the crack resistance of the compounds, J_c. For the indirect tensile tests, circular specimens, 50 mm in diameter and 12.7 mm thickness were used. All specimens were left to cure under water for 7 days. A 2.5-fold increase in the indirect tensile strength was achieved at an ETM loading of 0.35% by weight. A nearly threefold increase in the fracture resistance occurred at the 0.1% ETM loading. The thermal resistivity of the compounds increased by 30% for a 1% Expancel loading. Fracture surface examination revealed that the ETM facilitated the permeation of water by creating pores. Thus, an optimum strength and fracture resistance was achieved between 0.1% and 0.4%.