Effects of Nano‐SiO₂ and SAP on Hydration Process of Early‐Age Cement Paste Using LF‐NMR

Abstract

The effects of nano-SiO2 and superabsorbent polymer on the hydration process of early-age cement paste are investigated through the physically bound water evolution test by means of the low-field nuclear magnetic resonance technology. The test results show that the hydration process can be characterized by four-stage patterns based on the zero points of the second-order differential hydration curve, i.e., the initial, accelerated, decelerated, and steady periods. The beginning time of each stage is postponed and the hydration duration is prolonged with an increasing water to cement ratio. The beginning time of each stage and the hydration duration are shortened with an increasing content of nano-SiO2. And the beginning time of each stage and the hydration duration are prolonged with an increasing content of superabsorbent polymer. Based on the test data and the Avrami–Erofeev model, a modified hydration model taking the influence of nano-SiO2 and SAP into account is proposed, and the predicted results are consistent with the test results.

The Stabilization Mechanism of Nano-SiO2 Precursor Solution

“…It can be seen from Figure 7 that a thin layer of flocculent substances is produced on the surface of cement particles [ 33 ]. These flocculent hydrated substances cover the surface of cement particles like gauze, which makes the surface of cement particles uneven, and the structure is open and porous [ 34 ]; in addition, many interlaced hydration products are generated in the pores of cement particles, so there are many obvious gaps and pores in the cement-based materials, which makes cement particles are not closely connected [ 30 ].…”

“…It can be seen from Figure 8 that cement hydration is accelerated, and that surfaces of cement particles are wrapped by planar flocculating substances with smooth surfaces [ 35 ], dense structures, and small pores. These flocculation substances and network C-S-H gels not only make cement particles more cohesive [ 30 ] but also fill the gaps among cement particles, reducing the gaps and pores among cement particles. Therefore, cement particles are closely connected with each other, which is advantageous for improving the density of cement-based materials [ 13 , 32 ].…”

“…Subsequently, the precursor solution of NS was added to the cement paste [ 27 ]. The precipitation morphology of the precursor solution in the cement paste and the energy spectrum of the reaction of the mixture was analyzed by performing scanning electron microscopy (SEM) measurements [ 26 , 28 , 29 , 30 , 31 ].…”

Comparative Overview of the Performance of Cementitious and Non-Cementitious Nanomaterials in Mortar at Normal and Elevated Temperatures

“…In experimental studies, ordinary Portland cement (OPC) at strengths of 42.5 or 52.5 MPa according to ASTM specifications is often used in cement mortar [ 69 , 70 , 71 , 72 ]. Generally, OPC Type I, Grade 42.5 N is used, conforming to ASTM C-150 [ 73 , 74 , 75 , 76 ].…”