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

Improving properties of supersulfated cement by regulating its physiochemical features through nanoSiO2-modification

Supersulfated cement (SSC) has been known as a low-carbon cementitious materials due to its low-clinker requirement but high-slag consumption. However, the slow property gain rate, especially at the early ages, together with the long-term drawbacks introduced by the physiochemical characteristics of SSC, has primarily blocked its application. In this work, a novel property-gain regulation technique by applying nanoSiO2 (NS) modification on the binding system was reported. Firstly, the macro-property of SSCs with NS was presented, and then the hydration features, as well as the physiochemical properties, were reported. It was found that 3 wt.% NS addition could increase the 90-day compressive strength of SSC to 100%, and the critical pore threshold value can be reduced by an order of magnitude. Quantitative analysis results showed that the modification of the chemical compositions and the variation of the resulting binders contribute to these significant changes. All these results highlighted a novel technique of developing a low-carbon cementitious binder with good performance through nano-engineering

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

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

Surface Treatment of Cement-Based Materials with NanoSiO2

A dense surface structure of cement-based material is favorable for its resistance to the impacts of environment. In this work, effectiveness and mechanisms of the surface treatment of cement-based materials with nanoSiO2 of different states, that is, colloidal nanoSiO2 (CNS) and the in situ formed nanoSiO2 gel through the hydrolysis of its precursor of tetraethoxysilane (TEOS), by brushing and soaking techniques, were investigated. Results showed that both CNS and TEOS are capable of reducing the liquid and gaseous transport properties of hardened cement-based materials, although at a different extent. It revealed that the pozzolanic reactivity and the filler effect of nanoSiO2 are the main causes for the refining of the threshold size and the reduction of volume of the capillary pores, and they finally lead to a linearly reduction of the transport property. From this study, it can be reflected that surface treatment of cement-based materials with nanoSiO2 would be an optimal alternative of making concrete structure more durable

Modification of Cement-Based Materials with Nanoparticles

This is a summary paper on the work being done at the Center for Advanced Cement-Based Materials at Northwestern University on the modification of cement-based materials with nanoparticles, specifically nanoclays, calcium carbonate nanoparticles, and nanosilica. The rheological properties of clay-modified cement-based materials are investigated to understand the influence of nanoclays on thixotropy. The influence of the method of dispersion of calcium carbonate nanoparticles on rate of hydration, setting, and compressive strength are evaluated. And an in-depth study on the mechanisms underlying the influence of nanosilica on the compressive strength gain of fly ash–cement systems is discussed. The motivation behind these studies is that with proper processing techniques and fundamental understanding of the mechanisms underlying the effect of the nanoparticles, they can be used to enhance the fresh-state and hardened properties of cement-based materials for various applications. Nanoclays can increase the green strength of self-consolidating concrete for reduced formwork pressure and slipform paving. Calcium carbonate nanoparticles and nanosilica can offset the negative effects of fly ash on early-age properties to facilitate the development of a more environmentally friendly, high-volume fly ash concrete

Effect of Nanosilica on the Sulfate Attack Resistivity of Cement Mortar

The effect of nanosilica on the sulfate attack resistivity of cement mortar was investigated through study on the mechanical property evolution and the length change of the cement mortar under 5 wt.% sodium sulfate for 6 months. Meanwhile, the effects were compared with those of fly ash-replacement mortar. Results showed that by taking the advantages of nanosilica and fly ash in improving the property of cement mortar at early and later ages, the sulfate attack resistance of cement mortar can be enhanced in mechanical property increase and expansion reduction. Further, it implies that a combination of both pozzolans could enhance the sulfate attack resistivity of cement-based materials

Effects of Colloidal NanoSiO2 on Fly Ash Hydration

The influences of colloidal nanoSiO₂ (CNS) addition on fly ash hydration and microstructure development of cement–fly ash pastes were investigated. The results revealed that fly ash hydration is accelerated by CNS at early age thus enhancing the early age strength of the materials. However, the pozzolanic reaction of fly ash at later age is significantly hindered due to the reduced CH content resulting from CNS hydration and the hindered cement hydration, as well as due to a layer of dense, low Ca/Si hydrate coating around fly ash particles. The results and discussions explain why the cementitious materials containing nanoSiO₂ had a lower strength gain at later ages. Methods of mitigating the adverse effect of nanoSiO₂ on cement/FA hydration at later ages were proposed

Novel Evidence for the Formation of Semi-Permeable Membrane Surrounding the Portland Cement Particles During the Induction Period

This letter presents strong novel evidence for the semi-permeable membrane surrounding Portland cement during the induction period. In the cement hydration, heat curve obtained through high-resolution differential scanning calorimetry under isothermal conditions, one main and some other smaller endothermic peaks were detected. These endothermic peaks are believed to be caused by the osmotic expansion that occurs after the semi-permeable membrane forms, not the precipitation of calcium hydroxide or the imbibition of water during the induction period