Abstract
In this study, the setting property and mechanical strength of cement pastes containing accelerators (CPCA) with or without superabsorbent polymers (SAPs) were first studied. The early microstructure evolution and water distribution at 7 and 28 days were probed by 1D (T2) and 2D (T1-T2 maps) H1 nuclear magnetic resonance (NMR) relaxometry, and the microstructure was systematically investigated by using mercury intrusion porosimetry (MIP), back-scattered electron (BSE) image and energy-dispersive X-ray spectroscopy (EDX) analysis. Results showed that the SAPs in the cement paste containing accelerators had various influences on setting time and compressive strength depending on the type of accelerators. The presence of SAPs in the cement paste containing alkaline free accelerators could alleviate the decrease of internal relative humidity, promote hydration and help to modify the pore structure. Moreover, it was observed that the SAP cavities could be nicely filled with calcium hydroxide (CH) in the cement paste with alkaline free accelerators.
Highlights
Sprayed concrete is a kind of commonly used material, which can form homogeneous structures with proper thickness, as well as sufficient rigidity and strength in a very short time
superabsorbent polymers (SAPs) led to an increase of 4.76% in compressive strength of the sample when compared to CPCA2 at a
These results suggest that the SAPs in cement paste containing alkaline free accelerator may contribute to forming a denser pore structure and reducing the internal relative humidity decrease
Summary
Sprayed concrete is a kind of commonly used material, which can form homogeneous structures with proper thickness, as well as sufficient rigidity and strength in a very short time. The design of sprayed concrete involves the components of cement paste containing accelerators (CPCA), densely packed aggregates (size generally below 16 mm) and an appropriate water to cement ratio (this depends on the demanding strength) [1,2]. To improve properties of CPCA, i.e., viscosity or setting time, a high dosage of accelerators and high content of binder materials are always used in practice. The high content of binder materials will result in a high cost and difficulties in manufacture and increases the autogenous shrinkage of sprayed concrete [2,3]. As proposed in Snashall’s [5] and Jensen’s patents [6], the use of superabsorbent polymers (SAPs) will increase viscosity and decrease the rebound of wet-mix sprayed concrete. It was observed that the uptake of water by SAPs created a change in viscosity
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