Use of superabsorbent polymers in the production of frost resistant concrete

For outdoor concrete structures in cold regions, additional air-filled spaces are normally created in concrete to protect concrete structures from frost damage. To ensure frost resistance of concrete, it is of importance to quantitatively evaluate the void structure in hardened concrete. In this thesis, the shape from focus (SFF) method is proposed to capture the depth information of the concrete surface. Based on the performance of focus measure operators and window sizes, the selected operator and window size are used to carry out the SFF analysis of the examined surface. The voids are identified based on the reconstructed depth map. Then the void parameters are determined by an automated analysis. The results demonstrate that the SFF method can be used for automated analysis of the void parameters without contrast enhancement.

Contrary to conventional air entraining agents (AEA), superabsorbent polymers (SAP) can be used to engineer the void structure in concrete, which may counteract the strength loss of frost resistant concrete. Also, internal curing provided by SAP may increase the concrete strength. However, the frost behaviours of concrete containing SAP are still not fully understood. In this thesis, the calorimetric freeze-thaw response of liquids in SAP in a cementitious environment is studied. Compared to the bulk exposure liquids, the freezing and melting peaks of liquid in SAP occur at lower temperatures. And the freezing and melting peaks of the liquids in SAP are likely influenced by several factors, e.g., the presence of ice-nucleating agents, the ion concentration in the exposure liquids, the moisture state of SAP, repeated absorption and desorption of SAP, and repeated freezing and thawing. The freezing and melting peak temperatures of liquids in SAP decrease with the decrease of the liquid/SAP ratio in SAP. And a good correlation is observed between the proportion of freezable water in SAP and the freezing and melting peak temperatures.

SAP is used to formulate the void structure in cement mortars. The deformation and phase transition of the capillary saturated mortars cooled to -85ºC are studied by combined calorimetry and dilatometry. The deformation of the mortars indicates that SAP voids can protect the mortars from frost damage in the same way as entrained air voids and voids created by polymeric microspheres (MS). The ice formation process in mortar containing SAP is different compared to air-entrained mortar and mortar containing MS, and it can be affected by the particle size and dosage of SAP. Significant expansion at -40ºC seems to not cause permanent damage to all mortars. The relation between the void parameters and the residual strain of the mortars is summarized, providing recommendations on the void structure when the mortars are subjected to very low temperatures.

Frost resistant concrete with SAP shows a higher compressive strength than frost resistant concrete with AEA. Life cycle assessment is employed to assess the overall environmental impact of different types of frost resistant concrete. When the strength and durability of concrete are considered in the functional unit, the environmental load of frost resistant concrete with SAP is generally lower than frost resistant concrete with AEA. Frost resistant concrete with SAP reduces the environmental impact of the vertical elements (e.g., columns), but it increases the environmental burdens of the horizontal elements (e.g., slabs). In addition, the life cycle inventory data for AEA and SAP can influence the impact assessment results.