Polymer-modified Cement Mortar Research Articles

Flexural behaviour of reinforced concrete beams repaired with styrene—butadiene rubber latex, silica fume and methylcellulose repair formulations

The use of plain cement mortar in repair works is limited to unimportant works because of its poor adhesive bond to the substrate and its performance from the point of view of durability. Polymer-modified cement mortar has replaced plain mortar for these reasons. Also, the incorporation of silica fume and methylcellulose in repair systems has been found to provide a better durability and overall performance. This paper presents the results of an experimental investigation of the flexural behaviour of six reinforced concrete beams. Five beams were repaired using five different repair systems, namely plain cement mortar and mortars modified with latex (L), latex and silica fume (L—S), latex silica fume and methylcellulose (L—S—M), and silica fume and methylcellulose (S—M). The sixth beam was an unrepaired control beam. The repair procedure was carried out while loading the beams, to match the on-site practice. The size of the beams was 100 X 150 X 1200 mm and they were reinforced with two 10 mm diameter steel rods with a yield strength of 551 MPa. The test results showed that beams repaired with L, L—S and L—S—M mortars successfully restored the structural capacity of the unrepaired beam, besides improving the durability, crack pattern and toughness characteristics of these beams. The use of plain or S—M mortars showed a poor structural performance since they exhibited early separation along the contact interface with the substrate, as well as reduced ductility and toughness.

The effect of polymer addition on the electrical behavior of ordinary and pulverized fly ash modified cement mortars

The electricla behavior of polymer-modified cement mortars has been evaluated as a function of the polymer and the evaporable water contents. The effects have been correlated to microstructural changes induced by the addition of an acrylic polymer and an epoxy resin purposely formulated for cement-based composites. Moreover, the effect of the addition of pulverized fly ash, which has proved to be beneficial on many of the cement composite properties, has also been studied. Polymer modified cement mortar composites exhibit a tendency towards insulating behavior which is greatly enhanced by water losses: the electrical properties must thus be carefully evaluated when static charge accumulation is not desired. The addition of pulverized fly ash to ordinary Portland mortars slightly influences the electrical behaviour, but strongly enhances the insulating behaviour of polymer modified cement mortars.

Prevention of air void formation in polymer-modified cement mortar by pre-wetting

The air voids that form when cement and aggregates are mixed with an aqueous polymer solution are not easily removed because they tend to be stabilized by the polymer. Antifoaming agents can be used to prevent air void formation, but they often cause problems of poor adhesion. An alternative approach is suggested for reducing air void formation in polymer-modified mortar, which is to pre-wet the cement and sand with water, and then add a concentrated polymer solution. The air content of a PVA-modified cement mortar prepared in this way was as low as 6%, which was lower than the 13% air content of the PVA-modified mortar with an antifoaming agent, and it was much lower than the 32% air content when a PVA solution was mixed with dry cement and sand.