Heat-Induced Acceleration of Pozzolanic Reaction Under Restrained Conditions and Consequent Structural Modification

A review of utilization of industrial waste materials as cement replacement in pervious concrete: An alternative approach to sustainable pervious concrete production

Around 8% of the global carbon dioxide emissions, are generated during cement manufacturing, which also involves significant use of raw materials, leading to adverse environmental effects. Consequently, extensive research is being conducted worldwide to explore the feasibility of utilizing different industrial waste by-products as alternatives to cement in concrete production. Fly ash (FA), Metakaolin (MK), Silica fume (SF), and ground granulated blast furnace slag (GGBS) are potential industrial materials that can serve as cement substitutes in pervious concrete. However, there exist conflicting findings in the literature regarding the impact of industrial supplementary cementitious materials (ISCMs) as partial cement replacements on the physical, mechanical, and durability properties of pervious concrete. The aim of this review is to investigate the feasibility and potential benefits of using ISCMs and compare them as partial cement replacements in the production of pervious concrete. The analysis primarily examines the effect of ISCMs as partial cement replacements on cementitious properties, including properties of ISMCs, mechanical properties, and durability of pervious concrete. The influence of ISCMs primarily stems from their pozzolanic reaction and filler characteristics. SF has the highest reactivity due to its high surface area and amorphous structure, resulting in a rapid pozzolanic reaction. GGBS and FA have moderate reactivity, while MK has relatively low reactivity due to its crystalline structure. Results from various studies indicate that the addition of FA, SF, and MK up to approximately 20% leads to a reduction in porosity and permeability while improving compressive strength and durability due to the filler effect of SF and MK. Incorporating GGBS increases permeability slightly while causing a slight decrease in compressive strength. The range of permeability and compressive strength for pervious concrete incorporating FA, SF, GGBS and MK were 0.17-1.46 cm/s and 4-35 MPa, 0.56-2.28 cm/s and 3.1-35 MPa, 0.19-0.64 cm/s and 8-42 MPa, 0.10-1.28 cm/s and 5.5-41 MPa, respectively, which are in the acceptable range for non-structural application of pervious concrete. In conclusion, it is possible to produce sustainable pervious concrete by substituting up to 20% of cement with FA, SF, GGBS, and MK, thereby reducing cement consumption, carbon footprint, energy usage, and air pollution associated with conventional cement production. However, further research is required to systematically assess the durability properties, long-term behavior, and, develop models for analyzing CO2 emissions and cost considerations of pervious concrete containing ISMCs.

Investigation on Roles of Packing Density and Water Film Thickness in Synergistic Effects of Slag and Silica Fume

The ternary blended cement with finer slag and silica fume (SF) could improve the packing density (PD) through the filling effect. The excess water (water more than needed for filling into voids between the cement particles) can be released to improve the fresh properties and densify the microstructure which is beneficial for improving the hardened properties. To verify the hypothesis and reveal how and why (cement + slag + SF) the ternary blends could bring such advantages, the binder pastes incorporating slag and SF with various water-to-binder ratios were produced to determine the PD experimentally. To evaluate the optimum water demand (OWD) for maximum wet density, the influence of the dispersion state of the binder on PD was investigated using the wet packing density approach. The effect of PD of various binary and ternary binder systems on water film thickness (WFT), fluidity, setting time, and compressive strength development of cement paste was also investigated. The results show that the ternary blends could improve the PD and decrease the water film thickness (WFT). The enhanced PD and altered WFT are able to increase fluidity and compressive strength. The ternary blends could improve the compressive strengths by increasing PD and exerting nucleation and pozzolanic effects.

A Study on the Cement Gel Formation Process during the Creation of Nanomodified High-Performance Concrete Based on Nanosilica

One of the most science-intensive and developing areas is nano-modified concrete. Its characteristics of high-strength, high density, and improved structure, which is not only important at the stage of monitoring their performance, but also at the manufacturing stage, characterize high-performance concrete. The aim of this study is to obtain new theoretical knowledge and experimental-applied dependencies arising from the “composition–microstructure–properties” ratio of high-strength concretes with a nano-modifying additive of the most effective type. The methods of laser granulometry and electron microscopy are applied. The existing concepts from the point of view of theory and practice about the processes of cement gel formation during the creation of nano-modified high-strength concretes with nano-modifying additives are developed. The most rational mode of the nano-modification of high-strength concretes is substantiated as follows: microsilica ground to nanosilica within 12 h. A complex nano-modifier containing nanosilica, superplasticizer, hyperplasticizer, and sodium sulfate was developed. The most effective combination of the four considered factors are: the content of nanosilica is 4% by weight of cement; the content of the superplasticizer additive is 1.4% by weight of cement; the content of the hyperplasticizer additive is 3% by weight of cement; and the water–cement ratio—0.33. The maximum difference of the strength characteristics in comparison with other combinations ranged from 45% to 57%.

Elucidation of the Hydration Reaction of UHPC Using the PONKCS Method

This study explored the hydration reaction of ultra-high-performance concrete (UHPC) by using X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA) as analysis methods. The partial- or no-known crystal structure (PONKCS) method was adopted to quantify the two main amorphous phases of silica fume and C-S-H; such quantification is critical for understanding the hydration reaction of UHPC. The measured compressive strength was explained well by the degree of hydration found by the PONKCS method, particularly the amount of amorphous C-S-H. During heat treatment, the pozzolanic reaction was more intensified by efficiently consuming silica fume. After heat treatment, weak but continuous hydration was observed, in which the cement hydration reaction was dominant. Furthermore, the study discussed some limitations of using the PONKCS method for studying the complicated hydration assemblage of UHPC based on the results of TGA and NMR. Generally, the PONKCS method underestimated the content of silica fume in the early age of heat treatment. Furthermore, the structural evolution of C-S-H, confirmed by NMR, should be considered for more accurate quantification of C-S-H formed in UHPC. Nevertheless, PONKCS-based XRD could be useful for understanding and optimizing the material properties of UHPC undergoing heat treatment.