Chloride binding in concrete: recent investigations and recognised knowledge gaps: RILEM Robert L’Hermite Medal Paper 2021

A theoretical understanding of chloride binding is urgently needed if we are to use the new low-CO2 composite cements in reinforced concrete structures exposed to chloride-loaded environments. The empirical models and “deemed-to-satisfy” rules currently in use will not help in the face of the wide variety of new SCMs now being proposed. Engineers need generic chloride ingress models that can handle the variations in binder chemistry and exposure conditions. This paper reviews a selection of recent investigations by a team of NTNU researchers and international collaborators on various Portland composite cements using a combination of equilibrium chloride-binding experiments and thermodynamic modelling. One of our main findings is that “leaching” simulated by varying the pH and the calcium concentration has a dominant effect on chloride binding. However, challenges regarding the quantification and characterization of the chloride binding phases have yet to be overcome. To advance in this field we need additional crucial thermodynamic data for chloride-binding hydrates formed by low-CO2 cements containing SCMs, and we need to overcome some experimental challenges. A major break-through would come from understanding the interactions between chlorides and C(-A)-S-H. Part of the answer might be found at the atomic level. Finally, mechanistic numerical models are needed to upscale the findings from chloride binding to chloride ingress models. We conclude by showing the significance of such theoretical work on chloride binding for engineers tasked with the construction and maintenance of the reinforced concrete structures that are so vital a part of modern infrastructure.

CO2 mineralization of demolished concrete wastes into a supplementary cementitious material – a new CCU approach for the cement industry

This contribution discusses the carbon capture and utilization (CCU) approach based on CO2 mineralization of cement paste from recycled concrete as new approach to capture CO2 and significantly contribute to the reduction in CO2 emissions associated with cement production. The current literature suggests that all CO2 released from the decomposition of limestone during clinker production can be sequestered by carbonation of the end-of-life cement paste. This carbonation can be achieved in a few hours at ambient temperature and pressure and with a relatively low CO2 concentration (< 10 %) in the gas. The carbonation of cement paste produces calcite and an amorphous alumina-silica gel, the latter being a pozzolanic material that can be utilized as a supplementary cementitious material. The pozzolanic reaction of the alumina-silica gel is very rapid as a result of its high specific surface and amorphous structure. Thus, composite cements containing carbonated cement paste are characterized by a rapid strength gain. The successful implementation of this CCU approach relies also on improved concrete recycling techniques and methods currently under development to separate out the cement paste fines and such. Full concrete recycling will further improve the circular utilization of cement and concrete by using recycled aggregates instead of natural deposits of aggregates. Although the feasibility of the process has already been demonstrated at the industrial scale, there are still several open questions related to optimum carbonation conditions and the performance of carbonated material in novel composite cements.

EFFECT OF LIMESTONE POWDER ON THE PROPERTIES OF BLENDED РORTLAND CEMENTS

The article shows the relation between sustainability and cement manufacture that can be obtained by the replacement of clinker with limestone additive. This decreases the use of energy resources and reduces CO2 emissions in cement production. The issue of partial Portland cement clinker substitution by finely ground limestone in the production of market-oriented types of cement type CEM II is solved on the cement plant PJSC "Ivano-Frankivsk Cement". The indexes of physical-mechanical tests of certified Portland limestone cement with high early strength CEM II/A-LL 42.5 R produced by PJSC "Ivano-Frankivsk Cement" are given. Finely dispersed limestone in Portland-composite cements with slag promotes a more complete synergic effect. It is established, that rapid-hardening blended Portland cements with limestone powder provide technological, technical, ecological, and economic effects in the production of prefabricated and monolithic reinforced concrete.

Developing a novel magnesium calcium phosphate/sodium alginate composite cement with high strength and proper self-setting time for bone repair

In this work, novel magnesium calcium phosphate/sodium alginate composite cements were successfully fabricated with a proper setting time (5–24 min) and high compressive strength (91.1 MPa). The physicochemical and biological properties of the cement in vitro were fully characterized. The composite cements could gradually degrade in PBS as the soaking time increase, and the weight loss reached 20.74% by the end of 56th day. The cements could induce the deposition of Ca–P layer in SBF. Cell experiments proved that the extracts of the composite cements can effectively promote the proliferation and differentiation of the mouse bone marrow mesenchymal stem cells (MSCs). These preliminary results indicate that the magnesium calcium phosphate/sodium alginate composite cements could be promising as potential bone repair candidate materials.

PRODUCTION OF COMPOSITE CEMENT BASED ON INDUSTRIAL WASTE

Проведены исследования физико-химических процессов структурообразования композиционных цементов с добавкой отходов обогащения полиметаллических руд современными методами. Были определены минералогический состав, химический состав с использованием рентгенофазового, микроскопического, дифференциально-термического методов анализа. Это позволило установить, что содержание карбонатов в отходах обогащения полиметаллических руд до 30% не понизило прочности образцов. Investigations of the physicochemical processes of structure formation of composite cements with the addition of wastes of concentration of polymetallic ores by modern methods have been carried out. The mineralogical composition, chemical composition were determined using X-ray phase, microscopic, differential thermal methods of analysis. This made it possible to establish that the carbonate content in the wastes of enrichment of polymetallic ores up to 30% did not reduce the strength of the samples.