Zonghui Zhou

The synergistic effect of nano-SiO2 with silica fume in cement-based material

To understand the synergistic effect of nano-SiO2(NS) and silica fume (SF) on cement-based material, the hydration process, the compressive strength development, and the pore structure of cement-based materials with the addition of nano-SiO2 and SF were investigated. The results showed that the compressive strength of cement paste increased with the increase of NS, especially at the early ages. Compared with 10% SF, the incorporation of 3% NS in the cement pastes with 7%wt dosage of SF has the highest compressive strength (51.93 MPa). When replace SF with 3% NS, the hydration of cement was promoted, C–S–H gel increased as more calcium hydroxide was consumed. Three percent NS and 7% SF can significantly reduce the porosity of the cement matrix, which is also an explanation of the phenomenon of increased compressive strength.

Effects of Nano-CaCO3 on the Properties of Cement Paste: Hardening Process and Shrinkage at Different Humidity Levels

The hardening process and volume stability of cement pastes with and without nano-CaCO3 (NC) were studied through investigations on the setting time and shrinkage. Results showed that NC shortened the setting time of cement paste: the initial setting time decreased by 3.9 and 11.1% when 1 and 3% NC were added, and the finial setting times were shortened by 6.2 and 15.2%, respectively. The shrinkage of cement paste was compensated by NC, and the effect was more obvious as more NC was added into the cement paste. Although the shrinkage decreased at the lower relative humidity, the degree of hydration of cement can be hindered owing to the lack of sufficient internal curing humidity. Considering the hydration of cement and the volume stability of structure, a high curing humidity was an important factor for improving the durability of NC-modified cement-based materials.

Influence of silica-based hybrid material on the gas permeability of hardened cement paste

Surface treatment is one of the most effective ways to elongate the service life of concrete. The surface treatment agents, including organic and inorganic types, have been intensively studied. In this paper, the silica-based hybrid nanocomposite, which take advantages of both organic and inorganic treatment agents, was synthesized and used for surface treatment of hardened cement-based material. The effectiveness of organic and inorganic hybrid nanocomposite was evaluated through investigations on the gas permeability of cement-based materials. The results showed that SiO2/PMHS hybrid nanocomposite can greatly decrease the gas transport properties of hardened cement-based materials and has a great potential for surface treatment of cementitious materials.

Deformation of a concrete matrix subject to a cyclic freeze–thaw process

The cyclic freeze–thaw process has been recognized as one of the most primary factors leading to structural and function failure of concrete. Strain, which may have certain inherent advantages when compared to traditional test parameters such as real-time non-destructive monitoring, which is more accurate and continuous with little error caused by manual intervention, was used to characterize the deformation and deterioration of a concrete matrix under a cyclic freeze–thaw process in this study. With the cyclic freeze–thaw process, the strain hysteretic loop is raised upwards indicating that residual strain is generated in the concrete matrix. The residual strain generated proves that damage in the concrete matrix is continuously accumulated and an irreversible deterioration process. The variation of freeze characteristic temperature ΔTf and the apparent frost heaving coefficient Δαf defined in this study can be used to characterize the degree of freeze–thaw damage and the frost resistance of concrete, respectively. Through theoretical analysis, a numerical model, which can show the relationship between concrete freeze–thaw damage and residual strain has been deducted and verified, which indicates that residual strain can be used to characterize the frost resistance of concrete subjected to a cyclic freeze–thaw process such as traditional parameters. Moreover, the residual strain generated in 3.5 wt% NaCl solution is larger than in water, showing that chloride attack accelerates the freeze–thaw damage of concrete.

Effect of Nano-SiO2 Content on the Setting Time and Mechanical Properties of Tricalcium Silicate

Using analytically pure calcium carbonate and silica as raw materials, high purity tricalcium silicate (C3S) is prepared by solid-state reaction. The tricalcium silicate was sintered at a temperature of 1550°C with the heat preservation time of 6 h. The final sample needs three times of calcination circles. Ultrasonic cleaning machine was used to disperse the water and different amount of nano-SiO2 (0, 1, 2, and 3 wt%) for 5 min, then mixed with C3S, and formed into standard blocks. The setting time and compressive strength of each age (1, 3, 7, and 28 days) was measured to investigate the effect of nano-SiO2 on the setting time and mechanical properties of C3S. The results show that the content of free calcium oxide (f-CaO) in C3S sample is lower than 0.8% tested by glycol ethanol method sensitive, C3S crystal type is triclinic system T1 by X ray diffraction (XRD). The nano-SiO2 cut down the setting time of C3S and the setting time of C3S is decreasing with the increasing content of nanoSiO2. The initial setting time of C3S with different content of nano-SiO2 (0, 1, 2, and 3 wt%) are 187, 129, 105, and 85 min, respectively, the final setting time are 219, 194, 158, and 130 min. The addition of nano-SiO2 can significantly improve the early compressive strength of C3S, but the effect of nano-SiO2 on improving compressive strength of C3S is gradually weakened with the hydration of C3S.

Influence of the Surface Treatment of Hardened Cement Mortar with Colloidal Nano-Silica and TEOS

Two types of silicate material, tetraethoxysilane (TEOS) and colloidal nanoSiO2 (CNS), were applied for surface treatment of hardened cement mortar by exploring their filling and pozzolanic reactivity to make the surface compacter. Results showed that the water adsorption coefficient, the water vapor transmission rate, and the water penetration depth were reduced when CNS and TEOS were applied onto the surface of hardened cement mortar, and TEOS exhibits a superior effect on surface treatment, making the mass-transport rate and extent smaller than CNS does.

The Promotion of Nano-SiO2 on the Compressive Strength of Alkali-Activated Materials

Nanomaterial which has high activity is widely used in the modification of cement-based materials due to its physical filling and chemical bonding. This paper mainly studied the influence of nano-SiO2 on the compressive strength of the alkali-activated materials, using XRD and SEM technology to analyze the mineral composition microstructure of alkali-activated materials, modification effect, etc. The results show that the doping of nano-SiO2 can enhance the compressive strength of alkali-activated materials. Under the condition of fixed water-binder ratio and alkali content, the optimum dosage of nano-SiO2 is 4%. When the content is 4%, the intensity of 28 days is increased by 26.81% compared with the blank sample, and compressive strength of 94.93 MPa is reached. By XRD and SEM, we can find a large number of CSH and a certain amount of CH in the sample. The promotion effect of nano-SiO2 on the alkali-activated materials provides a better support for the application of the alkali-activated materials in reality.

The Effect of Nano-SiO2 Dispersed Methods on Mechanical Properties of Cement Mortar

Nano-SiO2 is added to the cement by using different dispersion methods, through the macroscopic mechanical properties to characterize its dispersion in the cement, it can be used to explore the best experimental process. The results show that the compressive strength of cement samples with different dispersion methods is different. When the physical dispersion method is used, the intensity is not improved, but the ultrasonic dispersion method is the smallest, and the dispersion of nano-SiO2 is -9.11%. When the surfactant is used as dispersant, the dispersion of nano-SiO2 by Naphthalene water reducer is the best, and the compressive strength is increased by 6.68%. By using polymeric dispersing agent, polyethylene glycol has a certain effect on the dispersion of nano-SiO2, but it has some damage to the cement (set-retarder, etc.). Based on the above experiments, we have obtained the best dispersion method, which uses ultrasonic dispersion, and also needs to add naphthalene water reducer.

Influence of SiO2@PMHS on the Water Absorption of Cement Mortar as a Surface Treatment Agent

In this paper, the core–shell structured SiO2@PMHS hybrid nanoparticles were synthesized with tetraethoxysilane (TEOS) and polymethylhydrosiloxane (PMHS). And SiO2@PMHS core–shell nanoparticles were first used as a surface treatment agent for cement-based materials. The influence of SiO2@PMHS nanoparticles on the water absorption of hardened cement mortar with water-to-cement ratio of 0.6 was investigated. Results showed that the water absorption of cement mortar treated with SiO2@PMHS nanoparticles was decreased by 93.47% in comparison to the control sample.