The Role of Inorganic Polymer Technology in the Development of ‘Green Concrete’

Advances in alternative cementitious binders

New cements for the 21st century: The pursuit of an alternative to Portland cement

Geopolymerization is a developing field of research for utilizing solid waste and by-products. It provides a mature and cost-effective solution to many problems where hazardous residue has to be treated and stored under critical environmental conditions. Geopolymer involves the silicates and aluminates of by-products to undergo process of geopolymerization. It is environmentally friendly and need moderate energy to produce. This review presents the work carried out on the chemical reaction, the source materials, and the factor affecting geopolymerization. Literature demonstrates that certain mix compositions and reaction conditions such as Al2O3/SiO2, alkali concentration, curing temperature with curing time, water/solid ratio and pH significantly influences the formation and properties of a geopolymer. It is utilized to manufacture precast structures and non-structural elements, concrete pavements, concrete products and immobilization of toxic metal bearing waste that are resistant to heat and aggressive environment. Geopolymers gain 70% of the final strength in first 3–4 h of curing.

Mechanism of geopolymerization and factors influencing its development: a review

Global strategies and potentials to curb CO2 emissions in cement industry

For first time, an experimental and computational study has been conducted to define a structural model for the C-A-S-H gel forming in alkali-activated slag (AAS) pastes that would account for the mechanical properties of these materials. The study involved a comparison with the C-S-H gel forming in a Portland cement paste. The structure of the C-A-S-H gels in AAS pastes depends on the nature of the alkali activator. When the activator is a NaOH, the structure of the C-S-H gel falls in between tobermorite 1.4 nm with a mean chain length of five, and tobermorite 1.1 nm with a mean length of 14. When waterglass is the activator the structure of the C-A-S-H gel is indicative of the co-existence of tobermorite 1.4 nm with a chain length of 11 and tobermorite 1.1 nm with a chain length of 14. This very densely packed structure gives rise to excellent mechanical properties.

A model for the C-A-S-H gel formed in alkali-activated slag cements

Effect of Shrinkage-reducing Admixtures on the Properties of Alkali-activated Slag Mortars and Pastes

Effect of Superplasticizer and Shrinkage-Reducing Admixtures on Alkali-Activated Slag Pastes and Mortars

This study analyzes the behaviour of waterglass- or NaOH-activated slag mortars after carbonation. The effect of a superplasticizer based on vinyl copolymer and shrinkage reducing polypropylenglycol derivative admixtures on that process was also examined. The same tests were run on cement mortars for reference purposes. The mortars were carbonated in a chamber ensuring CO2 saturation for four and eight months, after which ages the samples were tested for mechanical strength; mercury porosimetry and mineralogical (XRD, FTIR) and microstructural characterization (SEM/EDX) were also conducted. The results obtained indicate that alkali-activated slag mortars were more intensely and deeply carbonated than Portland cement mortars. Carbonation took place directly on the gel, causing decalcification. When waterglass was the alkaline activator used, carbonation caused a loss of cohesion in the matrix and an important increase in porosity and decrease in mechanical strength. When a NaOH solution was used as the alkali activator, carbonation enhanced mortar compaction and increased mechanical strength. Finally, in waterglass-activated slag mortars, the inclusion of organic admixtures had no effect either on their behaviour after carbonation or the nature of the reaction products.

Carbonation process of alkali-activated slag mortars

A study was conducted on the effect of a polycarboxylate (PC) admixture on the mechanical, mineralogical, microstructural and rheological behaviour of Portland cement pastes. It was observed that the presence of PC admixture retards the initial cement hydration reactions, although this effect may be offset by possible increased diffusion in later stages. Additionally, the PC admixtures produce a few alterations in the structure and composition of the formed C—S—H gel. The addition of 1% PC admixture in the pastes generates a higher percentage of silicate bridge (Si Q2 units) mainly at 2 days. The admixture used in this study induced microstructural modifications in the pastes which slightly reduced the porosity; however the admixture did not affect the mechanical strength of the pastes at either 2 or 28 days of hydration. Finally, from the results of the rheological studies it was concluded that a low dosage of PC led to a substantial reduction (over 70%) in the yield stress.

/pdf/polycarboxylate-superplasticiser-admixtures-effect-on-1nrd1b1663.pdf

Marta Palacios

Papers

A model for the C-A-S-H gel formed in alkali-activated slag cements

Effect of Shrinkage-reducing Admixtures on the Properties of Alkali-activated Slag Mortars and Pastes

Effect of Superplasticizer and Shrinkage-Reducing Admixtures on Alkali-Activated Slag Pastes and Mortars

Carbonation process of alkali-activated slag mortars

Polycarboxylate superplasticiser admixtures: effect on hydration, microstructure and rheological behaviour in cement pastes