Estimating the Impact of Nanophases on the Production of Green Cement with High Performance Properties

Ordinary Portland cement (OPC) production is energy-intensive and significantly contributes to greenhouse gas emissions. One method to reduce the environmental impact of concrete production is the use of an alternative binder, calcium sulfoaluminate cement, which offers lower CO2 emissions and reduces energy consumption for cement production. This article describes the effect of adding nanophases, namely belite, calcium sulfoaluminate, calcium aluminum monosulfate (β-C2S, C4A3S, and C4AS, respectively) on OPC’s properties. These phases are made from nanosubstances such as nano-SiO2, calcium nitrate (Ca(NO3)2), and nano-aluminum hydroxide Al(OH)3 with gypsum (CaSO4·2H2O). The impact of β-C2S, C4A3S, and C4AS nanophases on the capabilities of cements was assessed by batch experimentations and IR, XRD, and DSC techniques. The results showed that the substituting of OPC by nano phases (either 10% C4A3S or 10% C4A3S and 10% β-C2S) reduced setting times, reduced the water/cement ratio and the free-lime contents, and increased the combined water contents as well as compressive strength of the cement pastes. The blends had high early and late compressive strength. The IR, XRD, and DSC analyses of the blends of 10% C4A3S or 10% C4A3S and 10% β-C2S cement displayed an increase in the hydrate products and the presence of monosulfate hydrate. The addition of 10% C4AS or 10% C4AS and 10% β-C2S to OPC reduced the setting times, decreased the W/C ratio, free lime, the bulk density, and increased the chemically-combined water and compressive strength. Overall, the results confirmed that the inclusion of the nanophases greatly enhanced the mechanical and durability properties of the OPCs.

Utilization of Sandy Soil as the Primary Raw Material in Production of Unfired Bricks

In this study, attempts were made to use sandy soil as the main raw material in making unfired bricks. The sprayed-cured brick specimens were tested for compressive and flexural strength, rate of water absorption, percentage of voids, bulk density, freezing/thawing, and water immersion resistance. In addition, the microstructures of the specimens were also studied using scanning electron microscope (SEM) and X-ray diffraction (XRD) technique. The test results show that unfired brick specimens with the addition of ground-granulated blast-furnace slag (GGBS) tend to achieve better mechanical properties when compared with the specimens that added cement alone, with GGBS correcting particle size distribution and contributing to the pozzolanic reactions and the pore-filling effects. The test specimens with the appropriate addition of cement, GGBS, quicklime, and gypsum are dense and show a low water absorption rate, a low percentage of voids, and an excellent freezing/thawing and water immersion resistance. The SEM observation and XRD analysis verify the formation of hydrate products C–S–H and ettringite, providing a better explanation of the mechanical and physical behavior and durability of the derived unfired bricks. The results obtained suggest that there is a technical approach for the high-efficient comprehensive utilization of sandy soil and provide increased economic and environmental benefits.

Experimental Study on the Performance and Microstructure of Cementitious Materials Made with Dune Sand

This paper presents the results of an investigation on the utilization of dune sand from waterway regulation engineering as the main raw materials to produce cementitious materials. The mechanical and durability properties of the cementitious materials were studied. Furthermore, a scanning electron microscope (SEM) and mercury intrusion porosimeter (MIP) were used to identify the microstructure of the specimens. The results show that the compressive and splitting tensile strength of cementitious materials can be improved due to the addition of ground granulated blast-furnace slag (GGBS) which mainly attributes to a better grain size distribution and pozzolanic effect compared to the specimen added cement alone. The specimen with the addition of suitable cement, GGBS, and gypsum shows low dry shrinkage and excellent abrasion resistance. Correspondingly the specimens present a lower porosity and total volume of pores at different curing ages. The SEM observation indicates that there are quite a lot of hydrate products such as calcium silicate hydrate gel in the matrix which verifies the formation of cementitious compounds. The results obtained suggest that there is potential in manufacturing cementitious material with dune sand in substitution of ordinary concrete to use in hydraulic engineering.

Pore Structure Analysis of Portland Cement and Blended Portland Cements Cured under Hydrothermal Conditions

The pore structure of Portland cement pastes cured under different hydrothermal regimes was analyzed. Pore size distribution (PSD), hydraulic permeability coefficient (HK) and porosity (P) were found depending on temperature and steam pressure. With increasing hydrothermal characteristics, the pore structures degraded causing the depletion in compressive strength. Then, blast furnace slag (BFS) and silica fume (SF) were added to PC and cured under similar conditions. It was found that the pore structure was greatly improved. The effect of hydrothermal curing may be interpreted by the intensity and position of the peak, by the length and bimodal characteristic of PSD. The maximum concentration of pores of reference cement paste lies in the range 10 – 103 nm, and changes progressively to the size < 10 nm with increasing addition of BFS and SF. This behavior is attributed mainly to the presence of SF. Microstructure analysis shows hydrate products like needle CSH and CASH, which were stable under hydrothermal curing.

On the Improvement of Fiber Reinforced Concrete through Surface Modification of Polypropylene by Grafting Method

Polypropylene (PP) fiber reinforced concrete is an important composite. In order to improve the mechanical properties of PP fiber reinforced concrete, polyacrylamide (PAM) was grafted onto the PP surface by the UV irradiation to enhance the hydrophilic property of PP in this study. IR spectra showed the existence of carboxylic acid functional groups on the treated PP surface. AFM images depicted that the treated PP surface had the lower height fluctuation, roughness, and had the acicular appearance. Contact angles of the treated PP were reduced in comparison with that of the original PP. All of these experimental results gave the evidences that PAM had been successfully grafted onto the treated PP surface. Furthermore, OM images depicted that the treated PP adhered to cement hydrate products (C-S-H) more tightly than that of the original PP did. We therefore expect that PP grafted with PAM can enhance mechanical properties of PP fiber reinforced concrete.

Infrared Spectrum Study of Autoclaved Systems with Solid Wastes

Different solid waste and their autoclaved waste samples were studied with the methods of infrared spectra (IR), X-ray diffraction (XRD) and chemical analysis. The results indicate that there is significant difference for strong absorbance Si-O bonds stretching vibration band of solid wastes infrared spectrum. The silicates have reacted and formed new hydrates which correspond to the strong absorbance Si-O bonds stretching vibration band. For containing activity crystal or amorphous which have ever been high-temperature heat such as fly ash, slag, waste glass and steel-slag, bound water amount of their autoclaved samples are related to strong absorbance Si-O bonds stretching vibration band, but there are no unity rules between the compressive strength of the autoclaved samples and strong absorbance Si-O bonds stretching vibration band because their type of hydrates products are significant differences. The IR characteristic peaks of waste concretes are almost same, and there are similar hydrate products (tobermorite and C-S-H (I) gel) and maximum compressive strength for different samples.

Effect of CCWC on the Self-Healing Action and the Microstructure of Cement-Based Materials

The performance of Capillary Crystalline Waterproofing Coatings(CCWC) was measured by its impermeability and self-healing ability. At the meantime, the microstructure of mortar treated by CCWC was researched with SEM and XRD. The results showed that Ionic transmission could cause a chemical reaction, generate a great quantity hydrate products to block up the pores and cracks in cement-based materials, endow it with self- healing ability, and increase its durability. With increment of the coverage rate, pores and cracks of cement-based materials can be better healed with ionic transmission.

Microstructural Development During Suspension Hydration of Tricalcium Silicate Under “Floating” and Fixed pH Conditions

ABSTRACTThe suspension hydration of tricalcium silicate (water-solid 500) has been studied under both floating and fixed pH (8 to 12) conditions. In addition to solution analysis, the microstructure and chemical composition of the hydrate products was also studied. The results are interpreted as suggesting the existence of two C-S-H phases in the system CaO-SiO2-H2O, the stabilization of each being dependent on the pH of the solution phase.