Synthesis of poly (2-acrylamido-2-methyl propane sulfonic acid) with high water absorbency and absorption under load (AUL) as concrete grade superabsorbent and its performance

Abstract Preparation and characterization of superabsorbent polymers (SAPs) of poly (2-acrylamido-2 methyl propane sulfonic acid) with different ratios of cross-linker/monomer (0.0043, 0.0086, 0.014, and 0.028) and swelling capacity on Portland cement properties and its hydration were investigated. The comparison between poly (AMPS) and commercial samples (agriculture and hygienic grade of SAP) was studied too. Synthetic and commercial grade SAPs were studied with FTIR (Fourier transform infrared spectroscopy), swelling (in distilled water and saline solution (0.9% NaCl, with pH 7)) and AUL (absorbency under load) were measured completely. As a result, poly (AMPS) with 0.03 g of cross-linker has the highest swelling capacity (425.52 g/g and 66.18 g/g in distilled water and saline solution respectively) and poly (AMPS) with 0.06 g of cross-linker shows the highest AUL (13.2 g/g) among the synthetic and commercial samples. The hydrations of cement paste were investigated by means of XRD (X-ray diffraction) and FTIR spectroscopy in combination with thermo analytical method (TGA/DTG) (Thermo gravimetric Analysis). To determine the crystal size and porosity, SEM-EDX (Scanning electron microscope-Energy-dispersive X-ray spectroscopy) was used and also, rheology was used to determine the workability and efficiency of cement paste. As it is concluded, the hydration of cement paste with agricultural SAP is better than the others. TGA shows that the intensity at 7 day hydration time is the most. The cement paste contains poly (AMPS) based SAP with higher amount of cross-linker (0.2 g) and low swelling content has the best workability. And the cement paste contains poly (AMPS) with low amount of cross-linker (0.03 g) and highest swelling had the lowest porosity and the best distribution. From viewpoint of workability A4 is the best and from viewpoint of swelling and microstructure of cement A1 is the best.