Photocatalytic Cementitious Material for Eco-Efficient Construction—A Systematic Literature Review

Interaction between composition and microstructure of cement paste and polymeric carbon nitride

NOx removal capacity and compressive strength of photocatalytic cementitious materials with various color properties

Because soluble salt in saline soil dissolves with water, utility tunnels built in saline soil foundation are more likely to damage due to by groundwater and earthquake. In this study, new cementitious composite materials were developed by using slag, building gypsum, quicklime, and magnesia. The unconfined compressive strengths of the saline soil solidified by new cementitious composite materials and cement are investigated, and the optimum proportion of the different components of the new cementitious composite materials is determined. We found from microscopic characteristics of the saline soil solidified by the new cementitious composite materials and cement that the new materials could better absorb chloride ions. Finally, the new cementitious composite materials were applied to saline soil foundation reinforcement of a utility tunnel. By using the finite element method (FEM) and shaking table tests, it can be seen that the displacement, acceleration and extent of damage of the utility tunnel after saline soil foundation reinforcement using new cementitious composite materials significantly decreased; therefore, the new cementitious composite materials can improve the seismic behaviour of the utility tunnel and shows potential future engineering application value.

Saline soil affected by earthquakes and groundwater can lead to subgrade subsidence and collapse in highway construction. Consequently, considering the potential activity of the waste slag and magnesia, new cementitious composite materials used in solid saline soil were developed in our study. The unconfined compressive strengths of the saline soil solidified by the new cementitious composite materials with a combination of magnesium oxide, calcium oxide, gypsum, and mineral powder and cement were investigated, and the optimum dosage proportion of the new cementitious composite material for solidifying saline soil was determined; then the SEM, EDS, and XRD of the saline soil solidified by the new cementitious composite materials and cement were analysed. The research result showed that the saline soil solidified by our newly developed cementitious composite material showed compact internal structure and uniformly distributed soil particles; moreover, the new cementitious composite material exhibited a favourable solidifying effect on harmful ions in saline soil, and the Cl− trapping capacity of the new cementitious composite materials was stronger than that of cement. Finally, our developed cementitious composite material was applied to saline soil subgrade strengthening, and the displacement, acceleration, excess pore water pressure, and damage degree of the subgrade strengthening by our newly developed cementitious composite materials decreased remarkably; therefore, our newly developed cementitious composite material can improve the seismic behaviour of the saline soil subgrade and show potential future engineering application value.

Experimental study on the properties of a polymer-modified superfine cementitious composite material for waterproofing and plugging

Quantification of hydroxyl radicals on cementitious materials by fluorescence spectrophotometry as a method to assess the photocatalytic activity

Significance of shrinkage-induced clamping pressure in fiber-matrix bonding in cementitious composite materials

Composites that use fly ash and slag as alkali-activated materials instead of cement can overcome the defects and negative effects of alkali-activated cementitious materials prepared with the use of an alkali-activated material. In this study, fly ash and slag were used as raw materials to prepare alkali-activated composite cementitious materials. Experimental studies were carried out on the effects of the slag content, activator concentration and curing age on the compressive strength of the composite cementitious materials. The microstructure was characterized using hydration heat, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), and its intrinsic influence mechanism was revealed. The results show that increasing the curing age improves the degree of polymerization reaction and the composite reaches 77~86% of its 7-day compressive strength after 3 days. Except for the composites with 10% and 30% slag content, which reach 33% and 64%, respectively, of their 28-day compressive strength at 7 days, the remaining composites reach more than 95%. This result indicates that the alkali-activated fly ash-slag composite cementitious material has a rapid hydration reaction in the early stage and a slow hydration reaction in the later stage. The amount of slag is the main influencing factor of the compressive strength of alkali-activated cementitious materials. The compressive strength shows a trend of continuous increase when increasing slag content from 10% to 90%, and the maximum compressive strength reaches 80.26 MPa. The increase in the slag content introduces more Ca2+ into the system, which increases the hydration reaction rate, promotes the formation of more hydration products, refines the pore size distribution of the structure, reduces the porosity, and forms a denser microstructure. Therefore, it improves the mechanical properties of the cementitious material. The compressive strength shows a trend of first increasing and then decreasing when the activator concentration increases from 0.20 to 0.40, and the maximum compressive strength is 61.68 MPa (obtained at 0.30). The increase in the activator concentration improves the alkaline environment of the solution, optimizes the level of the hydration reaction, promotes the formation of more hydration products, and makes the microstructure denser. However, an activator concentration that is too large or too small hinders the hydration reaction and affects the strength development of the cementitious material.

Abrasive waterjet (AWJ) material processing represents a relatively new and extremely efficient method in the specific industries, implying various applicability areas, attributed to different materials, with different properties and domains of use. Besides numerous advantages of the AWJ cutting and generally of the material processing techniques, they also involve the waste generation: the abrasive sands are converted into sludge material, collected into recipients and further on, after natural drying, they become waste dumps randomly deserted. The enlargement of the AWJ techniques in the latest years determines the corresponding increase of the associated Garnet wastes (Spent Garnets, SG), thus leading towards the clear need of identifying opportunities for their recycling and valorisation. Aggregates are basic raw materials in the production of concrete, mortar and plasters, composite cementitious and/or cement-free materials (geopolymer concrete) in the building materials and generally, in the construction industry. The rapid growth of the population, recorded mainly in urban areas, determines an increasing demand on housing facilities and consequently, on concrete production and aggregates consumption. Aggregates and sand, mainly exploited from riverbeds or quarries, represent exhaustible natural resource for which substitution solutions need to be found, in order to control and reduce their extraction from the natural landscape. Considering the superposition of this independent cause and effect situations, the rapid growth of Spent Garnets (SG) landfills, generated by AWJ processes, and, on the other hand, the need to substitute the natural aggregate in construction industry, a reliable solution could emerge from the potential valorisation of SG wastes as partial or even complete substitution of sands / aggregates in the composition of construction materials. The present paper offers a preliminary overview regarding the possibility of incorporating SG wastes of local production in usual cement-based materials, as partial substitute of the aggregate, for the double purpose of waste management implementation and natural resources protection, on the transition path towards the implementing the Circular Economy (CE) concept in the Romanian industry.

Cement-based ductile rapid repair material modified with self-emulsifying waterborne epoxy

Air pollution is a prominent critical issue of vehicles. The toxic pollutants are harmful to the environment, hazardous to human health and difficult to degrade by natural means. Therefore a significant amount of efforts have been done on road pavements that directly interact with vehicles. Basing on the synergetic effect of cement and titanium dioxide discovered in recent years new road pavements were developed. In particular, photocatalytic cementitious road materials can represent a key element to improve air quality, thanks to their ability to accelerate the natural reaction of oxidation. This paper deals with the development of several types of photocatalytic cementitious road pavements, such as paving blocks, asphalt concrete filled up with a photocatalytic slurry and concrete roads. Large laboratory and field-testing programs have been conducted measuring the environmental effectiveness by means of a specific set-up and in-situ sources, respectively. Functional and mechanical tests have also been performed on the materials studied to investigate their behavior under traffic loadings. Indeed, road pavements have to guarantee both de-polluting effects and performances usually required to a road pavement wearing course, according to the current Standards. The large research activity conducted till now clearly showed the significant contribution of such innovative materials to the improvement of air quality, reducing the nitrogen oxides concentration up to 60% in some local weather conditions. They can represent a new frontier of the research aimed at reducing air pollutants, for environmental friendly solutions. The findings underline the benefits of the inclusion of titanium dioxide in concrete pavements.

The hot-dry environment in high geothermal tunnels negatively affects the development of properties of cementitious materials. In order to improve the mechanical properties of cementitious materials in such environments, a proper curing system was developed, the material compositions were taken into account, and the related mechanism was analyzed by microscopic tests. The results showed that the mechanical properties and microstructure of cementitious materials can be improved effectively by adopting film curing and an adequate dosage of fly ash in a hot-dry environment. Compared with standard curing, a hot-dry environment accelerates the evaporation of water in fresh cementitious materials and the early hydration rate of cementitious materials, resulting in lots of unhydrated cement particles and an uneven distribution of hydration products, seriously decreasing the properties of the cementitious materials. Film curing keeps the water from evaporating and ensures enough water is available for hydration at an early age. The addition of FA reduces the amount of cement clinker and decreases hydration reaction rate in high temperature environments at an early stage, avoiding the unevenness of hydration products. High temperatures stimulate the pozzolanic activity of fly ash and promote the degree of secondary hydration reaction, producing more hydration products, as well as contributing to the improvement of the mechanical properties and microstructure of cementitious materials. In this study, in a hot-dry environment, the mechanical properties of mortar with 25% fly ash and 2–3 d film curing are better than those of other experimental groups, including those of standard curing.

Measurement of benzene, toluene, ethylbenzene and o-xylene gas phase photodegradation by titanium dioxide dispersed in cementitious materials using a mixed flow reactor

This paper examines the desorption of hydrogels in contact with porous cementitious materials to aid in understanding the mechanisms of water release from superabsorbent polymers (SAP) into cementitious materials. The dependence of hydrogel desorption on the microstructure of cementitious materials and relative humidity was studied. It was shown that the capillary adhesion developed at the interface between the hydrogel and cementitious materials increased the desorption of the hydrogels. The size of hydrogels was shown to influence desorption, beyond the known size dependence of bulk diffusion, through debonding from the cementitious matrix, thereby decreasing the effect of the Laplace pressure on desorption. Microscopic examination highlighted a stark contrast in the desorption morphology of hydrogels with different chemical compositions.

Various self-healing methods for concrete, such as the use of supplementary cementitious materials, adhesive agents, mineral admixtures, and bacteria, have been suggested to date, and each of these has merits and demerits. Among these, however, the use of cementitious materials may be appropriate due to their good healing efficiency, low cost, and compatibility with the cement matrix. In this study, granulation and coating methods were applied to a new cementitious composite material. The self-healing property of these materials was controlled by the polyvinyl alcohol (PVA) coating until cracks were created. Water dissolved the PVA coating after entering through the cracks, and reacted with the healing materials to generate healing products. The self-healing performance was evaluated at various elapsed times through the measurement of the crack widths, visual observation, and examination of the microscopic images. Simultaneously, a water permeability test was performed and the dynamic modulus of elasticity was measured to verify the recovery of the cracks. In addition, the healing products that had been formed in the cracks were analyzed via X-ray diffraction (XRD) and scanning electron microscopy (SEM).