Effect of some biotic factors on microbially-induced calcite precipitation in cement mortar

Sporosarcina pasteurii, a common soil bacterium has been tested for microbial treatment of cement mortar. The present study also seeks to investigate the effects of growth medium, bacterial concentration and different buffers concerning the preparation of bacterial suspensions on the compressive strength of cement mortar. Two growth media, six different suspensions and two bacterial concentrations were used in the study. The influence of growth medium on calcification efficiency of S. pasteurii was insignificant. Significant improvement in the compressive as well as the tensile strength of cement mortar was observed. Microbial mineral precipitation visualized by Scanning Electron Microscopy (SEM) shows fibrous material that increased the strength of cement mortar. Formation of thin strands of fillers observed through SEM micrographs improves the pore structure, impermeability and thus the compressive as well as the tensile strengths of the cement mortar. The type of substrate and its molarity have a significant influence on the strength of cement mortar

Effects of Redispersible Polymer Powder on Mechanical and Durability Properties of Preplaced Aggregate Concrete with Recycled Railway Ballast

The rapid-hardening method employing the injection of calcium sulfoaluminate (CSA) cement mortar into voids between preplaced ballast aggregates has recently emerged as a promising approach for the renovation of existing ballasted railway tracks to concrete tracks. This method typically involves the use of a redispersible polymer powder to enhance the durability of the resulting recycled aggregate concrete. However, the effects of the amount of polymer on the mechanical and durability properties of recycled ballast aggregate concrete were not clearly understood. In addition, the effects of the cleanness condition of ballast aggregates were never examined. This study aimed at investigating these two aspects through compression and flexure tests, shrinkage tests, freezing-thawing resistance tests, and optical microscopy. The results revealed that an increase in the amount of polymer generally decreased the compressive strength at the curing age of 28 days. However, the use of a higher polymer ratio enhanced the modulus of rupture, freezing-thawing resistance, and shrinkage resistance, likely because it improved the microstructure of the interfacial transition zones between recycled ballast aggregates and injected mortar. In addition, a higher cleanness level of ballast aggregates generally improved the mechanical and durability qualities of concrete

Carbon dioxide sequestration on mortars containing recycled aggregates: A hot area for startup development

The world is closer to exceeding the budget (cumulative amount of anthropogenic CO2 emission compatible with a global temperature-change target) for the long-term target of the Paris Climate Agreement than previously thought. Three lines of evidence suggest that global warming will be faster than projected in the recent IPCC special report.  First, greenhouse-gas emissions are still rising. Second, governments are cleaning up air pollution faster than the IPCC and most models previously assumed. But aerosols, including sulfates, nitrates and organic compounds, reflect sunlight so the aforementioned cleaning could have a warming effect by as much as 0.7 ºC. And in third place, there are signs that the planet might be entering a natural warm phase because the Pacific Ocean seems to be warming up. And these three forces reinforce each other. Carbon dioxide sequestration is therefore crucial for targets for limiting global warming. Europe is now putting great efforts and funding in carbon sequestration materials and technologies. The flagship programme EnCO2re, currently looks to develop new technologies offering novel ways to use CO2; increase awareness for CO2 re-use; and ensures sustainability and social acceptance of materials and products by integrated socio-ecological research. Also Carbon capture and sequestration is one of the 100 Radical Innovation Breakthroughs for the future (Europe, 2019)..This chapter discloses results of an investigation concerning the performance of fly ash/waste glass alkaline-based mortars with recycled aggregates reinforced by hemp fibres. The results show that hemp fibres lead to a reduction of mechanical properties of alkali-activated materials.Foundation for Science and Technology (FCT) in the frame of project IF/00706/2014-UM.2.1

Carbon dioxide sequestration of fly ash alkaline based mortars with recycled aggregates and different sodium hydroxide concentrations: Properties, durability, carbon footprint, and cost analysis

This chapter discloses results of an investigation concerning carbon dioxide sequestration on fly ash/waste glass alkaline-based mortars with recycled aggregates and different sodium hydroxide concentrations. Properties, durability, carbon footprint, and cost analysis were studied on it. Mixtures using a sodium hydroxide concentration of 8M and the additive calcium hydroxide show the best performance and the lowest carbon footprint. Simulations using a carbon tax of 0.0347 Euro/kg show no influence on the cost of the mixtures while the use of the carbon tax of 0.206 Euro/kg show an increase in the cost-efficiency of mixtures, even those using a sodium hydroxide concentration of 8M and additive calcium hydroxide.The authors would like to acknowledge the financial support of the Foundation for Science and Technology (FCT) in the frame of project IF/00706/2014-UM.2.15.info:eu-repo/semantics/publishedVersio

Value added utilization of by-product electric furnace ferronickel slag as construction materials: A review

This paper reviews the potential use of electric furnace ferronickel slag (FNS) as a fine aggregate and binder in Portland cement and geopolymer concretes. It has been reported that the use of FNS as a fine aggregate can improve the strength and durability properties of concrete. Use of some FNS aggregates containing reactive silica may potentially cause alkali-silica reaction (ASR) in Portland cement concrete. However, the inclusion of supplementary cementitious materials (SCM) such as fly ash and blast furnace slag as partial cement replacement can effectively mitigate the ASR expansion. When finely ground FNS is used with cement, it shows pozzolanic reaction, which is similar to that of other common SCMs such as fly ash. Furthermore, 20% FNS powder blended geopolymer showed greater strength and durability properties as compared to 100% fly ash based geopolymers. The utilization of raw FNS in pavement construction is reported as a useful alternative to natural aggregate. Therefore, the use of by-product FNS in the construction industry will be a valuable step to help conservation of natural resources and add sustainability to infrastructures development. This paper presents a comprehensive review of the available results on the effects of FNS in concrete as aggregate and binder, and provides some recommendations for future research in this field

Influence of slag composition on the stability of steel in alkali-activated cementitious materials

Among the minor elements found in metallurgical slags, sulfur and manganese can potentially influence the corrosion process of steel embedded in alkali-activated slag cements, as both are redox-sensitive. Particularly, it is possible that these could significantly influence the corrosion process of the steel. Two types of alkali-activated slag mortars were prepared in this study: 100% blast furnace slag and a modified slag blend (90% blast furnace slag? 10% silicomanganese slag), both activated with sodium silicate. These mortars were designed with the aim of determining the influence of varying the redox potential on the stability of steel passivation under exposure to alkaline and alkaline chloride-rich solutions. Both types of mortars presented highly negative corrosion potentials and high current density values in the presence of chloride. The steel bars extracted from mortar samples after exposure do not show evident pits or corrosion product layers, indicating that the presence of sulfides reduces the redox potential of the pore solution of slag mortars, but enables the steel to remain in an apparently passive state. The presence of a high amount of MnO in the slag does not significantly affect the corrosion process of steel under the conditions tested. Mass transport through the mortar to the metal is impeded with increasing exposure time; this is associated with refinement of the pore network as the slag continued to react while the samples were immersed

Nano reinforced cement paste composite with functionalized graphene and pristine graphene nanoplatelets

This study examines and compares the workability, hydration, mechanical, microstructure and transport properties of cement paste composites containing the three forms of graphene-based 2D nanomaterials synthesised from epigenetic graphite deposit, namely, graphene oxide (GO), reduced graphene oxide (rGO), and pristine graphene nanoplatelates (G). Graphene materials were used from 0.01% to 0.16% of cement weight. The rGO and G were treated with salt and surfactant, respectively during synthesis, to improve dispersion in water. Characteristics and physical strength vary among GO, rGO and G, which have influenced the properties of nano reinforced graphene-cement composites (GCCs). The 28-day compressive and flexural strength of graphene (GO, rGO and G) cement composite improved by 28% and 81%, 30% and 84%, and 39% and 38%, respectively, compared to the control mix (cement paste without graphene materials). Finally, microscopic analysis, dynamic vapour sorption (DVS), electrical resistivity and water sorptivity results suggested that graphene materials densify and reinforce the composite microstructure