EFFECTS OF MATERIAL SEPARATION OF POLYE-MODIFIED CEMENT WATERPROOFING MEMBRANES ON FATIGUE RESISTANCE OF JOINT AT SUBSTRATE

Abstract

 A polymer-modified cement waterproofing membrane is a construction material (PCWM) with a high polymer to cement ratio (P/C) of 100 to 200% by weight, which improves waterproofing and elongation performance. When PCWM is applied to horizontal surfaces such as roofs and floor slabs, the cement component will settle in the material due to the difference in specific gravity of polymer and cement. As a result, a significant amount of cement hydration products are expected to be present on the underside of the waterproofing membrane. When the water content is increased in order to conveniently improve the workability, there is a high risk of material separation. There is a concern that the crack followability of the substrate concrete, and fatigue resistance due to repetition of expansion and contraction of cracking due to changes in the environmental temperature will be reduced. Furthermore, when used outdoors, the performance will be affected by weathering caused by such influences as solar radiation and heat.

 In this study, the cross-sectional microstructure of PCWM was observed by scanning electron microscopy, and the state of material separation between cement and polymer was clarified. In addition, the relationship between the microstructure and substrate crack followability and fatigue resistance were investigated. As a test specimen for observation of the microstructure, a sheet shape waterproof membrane was prepared. Then, a sample was cut out for observation. In order to observe the cross-sectional direction, depth of grinding into the sample from the surface was controlled to expose the observation surface. 10 locations were observed at 0.2 mm intervals at a depth of 0.1 mm from the surface. Fatigue resistant test specimens were prepared measuring 100 mm wide, 380 mm long and 2.0 thick. PCWM was applied on the substrate slate plate. Cracks were generated in the substrate slate, which were then expanded and contracted to produce movement of the area just above the crack in PCWM. Movement consisted of three levels of; 0.25- 0.5 mm, 0.5-1.0 mm and 1.0-2.0 mm, respectively. The number of fatigue cycles was 1500 for each level, with a period of 0.5 Hz. During applying movement, condition of the cracks in PCWM was observed.

 From results obtained in these investigations, the following was concluded:

 (1) Difference in specific gravity between polymer and cement for constituting PCWM, depending on mix proportions, cement hydration products may settle at the bottom and cause non-uniformity in the material.

 (2) Tensile strength and elongation of PCWM with uneven distribution of materials are reduced even if the P/C is the same in the mix proportion.

 (3) Tensile strength and elongation rate were reduced due to the weathering. The higher P/C and W/B were strongly affected by weathering and the rate of reduction was greater.

 (4) The higher the tensile strength and elongation rate of PCWM, tended to increase substrate crack followability and crack-fatigue resistance. In the case where the non-uniformity PCWM, the fatigue resistance was reduced. On the other hand, even in the case of large P/C and deterioration of mechanical properties due to weathering, if the material was homogeneous, it retained good fatigue resistance.