A critical review of waste glass powder - Multiple roles of utilization in cement-based materials and construction products.

In light of concerns relating to improper waste disposal and resources preservation, reclamation of the discarded glass in construction materials had been extensively carried out since 1963. In the past decade, although more than 100 papers associated with the use of glass powder (GP) in the micron level scale were published, comprehensive review of all practical applications in cement-based materials and construction products is not available. This paper therefore provides a summary of the body of knowledge on the interaction and effects of using GP in cement-based and extended construction materials. This review concludes that GP is an innovative and promising eco-supplementary cementitious material. Beyond that, use of GP is demonstrated to be potentially beneficial as a precursor in geopolymer and suitable for manufacturing eco-cement, artificial lightweight aggregate and composite phase change material. The multiple applications of GP are seen as an important step towards waste glass recycling as a sustainable construction material and for the overall betterment of the industry.

In-situ conversion of geopolymer into novel floral magnetic sodalite microspheres for efficient removal of Cd(II) from water.

In the present work, a novel, floral-like, magnetic sodalite microsphere (SODM) was synthesized in situ by using fly ash (FA) and metakaolin (MK) as raw materials and was used to remove Cd(II) from water. Its magnetism can solve the problems of adsorbent recovery and possible secondary pollution. During the static adsorption, SODM shows a maximum adsorption capacity of 245.17 mg/g. The adsorption of Cd(II) on the SODM surface is spontaneous, exothermic, and physicochemical adsorption, which was evaluated by thermodynamics, kinetics, and isotherm studies. During dynamic adsorption, SODM shows a maximum adsorption capacity of 342.74 mg/g in the simulated solution prepared by the deionized water, compared to 215.88 mg/g in the simulated solution prepared using Xiangsi Lake water from Guangxi Minzu University. At 0.5 g SODM dosage in the dynamic adsorption, the adsorption capacity could rise to 632.81 mg/g. These results demonstrated the excellent Cd (II) adsorption performance of the SODM. The adsorption of cadmium on the SODM surface includes the synergistic effects of electrostatic attraction, ion exchange, and surface coordination reaction. Besides, the SODM shows good regeneration performance in both the deionized water and Xiangsi Lake water. The present study explores SODM as an adsorbent for the Cd (II) removal from wastewater and unbolts the industrial applicability of the SODM in the field of wastewater purification.

An Investigation of Softening Laws and Fracture Toughness of Slag-Based Geopolymer Concrete and Mortar.

This paper aimed to determine the softening laws and fracture toughness of slag-based geopolymer (SG) concrete and mortar (SGC and SGM) as compared to those of Portland cement (PC) concrete and mortar (PCC and PCM). Using three-point bending (TPB) tests, the load vs. mid-span displacement, crack mouth opening displacement, and crack tip opening displacement curves (P-d, P-CMOD, and P-CTOD curves) were all recorded. Bilinear softening laws of the PC and SG series were determined by inverse analysis. Furthermore, the cohesive toughness was predicted using an analytical fracture model. The cohesive toughness obtained by experimental study was consistent with that predicted by analytical method, proving the correctness of the tension softening law obtained from inverse analysis. In addition, both initial and unstable fracture toughness values of SG mortar were lower than those of PC mortar given the same compressive strength. Moreover, the initial fracture toughness of SG concrete was generally lower than that of PC concrete, whereas the unstable fracture toughness exhibited an opposite trend.

Rheological Properties of Cement Paste with Nano-Fe3O4 under Magnetic Field: Flow Curve and Nanoparticle Agglomeration.

Understanding the influence of magnetic fields on the rheological behavior of flowing cement paste is of great importance to achieve active rheology control during concrete pumping. In this study, the rheological properties of cementitious paste with water-to-cement (w/c) ratio of 0.4 and nano-Fe3O4 content of 3% are first measured under magnetic field. Experimental results show that the shear stress of the cementitious paste under an external magnetic field of 0.5 T is lower than that obtained without magnetic field. After the rheological test, obvious nanoparticle agglomeration and bleeding are observed on the interface between the cementitious paste and the upper rotating plate, and results indicate that this behavior is induced by the high magnetic field strength and high-rate shearing. Subsequently, the hypothesis about the underlying mechanisms of nanoparticles migration in cementitious paste is illustrated. The distribution of the nanoparticles in the cementitious paste between parallel plates is examined by the magnetic properties of the powder as determined by a vibrating sample magnetometer. It is revealed that the magnetization of cementitious powders at different sections and layers provides a solid verification of the hypothesis.

Influence of interface conditions on the response of transversely isotropic multi-layered medium by impact load.

Multi-layered media are one of the most common phenomena in natural or artificial surroundings, and it is considered as a good candidates for biomedical applications. The transversely isotropic characteristic of materials have been widely recognized in elastic multi-layered media. Furthermore, interface conditions between transversely isotropic elastic multi-layered medium layers plays an important role in the medium's performance. Despite many numerical approaches in these analyses, very few theoretical methods are available in dealing with these two important issues. This study presents a method to compute the response of transversely isotropic elastic multi-layered medium subjected to the impact load, i.e. falling weight deflectometer load (FWD) load, when interfacial conditions are considered. Details of the mathematical derivation, implementation and verification of the proposed analytical solution are presented. The absence of positive exponential functions in the solution leads to a considerable improvement in computation efficiency and stability. Subsequent numerical results demonstrate that both transverse isotropy and interface conditions could substantially contribute to the responses of the elastic multi-layered medium.

Stabilization/solidification of hazardous and radioactive wastes with alkali-activated cements.

This paper reviews progresses on the use of alkali-activated cements for stabilization/solidification of hazardous and radioactive wastes. Alkali-activated cements consist of an alkaline activator and cementing components, such as blast furnace slag, coal fly ash, phosphorus slag, steel slag, metakaolin, etc., or a combination of two or more of them. Properly designed alkali-activated cements can exhibit both higher early and later strengths than conventional portland cement. The main hydration product of alkali-activated cements is calcium silicate hydrate (CSH) with low Ca/Si ratios or aluminosilicate gel at room temperature; CSH, tobmorite, xonotlite and/or zeolites under hydrothermal condition, no metastable crystalline compounds such as Ca(OH)(2) and calcium sulphoaluminates exist. Alkali-activated cements also exhibit excellent resistance to corrosive environments. The leachability of contaminants from alkali-activated cement stabilized hazardous and radioactive wastes is lower than that from hardened portland cement stabilized wastes. From all these aspects, it is concluded that alkali-activated cements are better matrix for solidification/stabilization of hazardous and radioactive wastes than Portland cement.

Laboratory development and field demonstration of self-sealing/self-healing landfill liner.

The self-sealing/self-healing (SS/SH) barrier concept is based on the principle that two or more parent materials placed in vertical or horizontal layers will react at their interfaces to form insoluble reaction products. These products constitute a seamless impermeable seal, which is resistant to the transmission of leachate and contaminants. A SS/SH liner formulation was developed in the laboratory and demonstrated at the Sudokwon landfill site in South Korea. Laboratory testing results indicated that a seal with a hydraulic conductivity less than 10(-9) m/s formed after two to four weeks of curing at room temperature, and the seal healed itself after it was fractured. The use of the soil from the Sudokwon landfill site instead of sand as the matrix of the parent materials in the SS/SH liner retarded the sealing and healing of the seal, but did not show an obvious effect on the overall sealing and healing capacity of the seal at early stages. The construction and installation of the field demonstration SS/SH liner were carried out in the same way as for a soil cement liner. The quality of the liner was ensured by the enforcement of quality analysis/quality control procedures during installation. A single sealed ring infiltration test was performed on the field demonstration liner 36 days after the installation was completed. The measurement of water infiltration rate indicated that the liner healed after it was fractured. However, the long-term sealing and healing capacity needs to be further investigated.