Pengkun Hou

Nano-modification of cementitious material: toward a stronger and durable concrete

Nanotechnology in construction and building materials has attracted great attention in recent years. Results demonstrated that nanomodification of cementitious materials can lead to significant improvement of the mechanical property, compactness, and durability. In this paper, based on the major characteristics of nanomaterials when used in cement-based materials, the recent progresses of nanomodification of cementitious materials with the mostly used nanomaterials such as nano-SiO2, nanoclay, nano-Al2O3,and carbon nano materials (carbon nanotubes and nanofibers) are reviewed. Modification effects and their influencing mechanisms of nanomaterials introduced by their specific features, such as the hydration seeding effect, the filling effect, the thixotropy-modifying effect, and the chemical reactivity feature on the properties of cementitious materials are reviewed. It is suggested that a stronger, greener, and more durable cementitious material can be obtained through the help of nanomodification.

Durability of Cement-Based Materials and Nano-particles: A Review

The development of modern cement and concrete industry calls for the improvement of the durability. By addition of a small amount of nano-particles nano structure of cement based materials can be modified and a higher durability can be achieved. In this paper, a review of the investigation of the effect of the frequently used nanoparticles, i.e., nano-silica, nano-clay and carbon nanotube on the durability of cement and concrete is presented. It is concluded that nanomodification of cementitious materials with nano-particle would make them durable through alteration of the physicochemical properties of the binder. Although intensive study on the usage of nano-silica has been conducted, more work is needed to get a better knowledge on the influencing mechanism. Surface-treatment of cementitous materials with nano-particles shows great potential for acquiring a durable concrete surface, and study on the selection of the treatment agent and treatment technique has been suggested. In addition, potential of using nano-clay in decreasing the transport property and the effect of carbon nanotube in optimizing the microstructure, as well as in decreasing the volume instability of cement-based materials are also discussed.

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.

A 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.

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.

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.

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.

Activation of Fly Ash through Nanomodification

Due to the high carbon emissions that result from cement production, it is desirable to limit the cement content of concrete to make it a more sustainable material. This is possible through substantial replacement of cement with supplementary materials, such as fly ash. The positive effects of this approach are twofold. First, reducing the cement content of concrete will reduce its carbon footprint. Second, fly ash is a coal combustion byproduct, so essentially a waste material, which must be stored in landfills and enclosures if unused. Therefore, the productive use of fly ash by incorporating it into building materials at high volumes can help alleviate a waste storage issue. This paper is a summary of studies performed at the Center for Advanced Cement-Based Materials - Northwestern University, in collaboration with Iowa State University, relating to the activation of fly ash through nanomodification. Through seeding effects and increased reactivity, nanoparticles can accelerate cement hydration and subsequently the production of calcium hydroxide (CH), which can help activate the pozzolanic reaction of fly ash particles. Two types of nanoparticles are discussed in this summary paper: silica (SiO²) and calcium carbonate (CaCO³). The study on CaCO³ nanoparticles addresses the issue of dispersion, which is critical for nanomaterials, and the resultant effects on the hardening and early-age properties of fly ash-cement pastes. And the study on nano SiO² focuses on determining the mechanisms underlying the effect of the pozzolanic nanoparticle on the early-age and long-term compressive strength gain of fly ash-cement mortars.