Durability of Green Concrete in Severe Environment

In this paper,the effects of different mineral admixtures and sulfate solution types on the appearance,mass change rate,relative dynamic elastic modulus,and corrosion resistance coefficient of concrete were systematically studied.X-ray Diffraction(XRD),Mercury Intrusion Porosimetry(MIP),Scanning Electron Microscopy(SEM),and X-ray Computed Tomography(X-CT)were used to explore and analyze the changes in the microstructure and the corrosion products of concrete in the sulfate solution.The results show that the existence of magnesium ions accelerates concrete deterioration.There is a critical dosage of fly ash for magnesium sulfate resistance of concrete.The magnesium sulfate resistance of concrete is improved when the fly ash content is less than 20%.Slag can significantly improve the corrosion resistance of concrete to magnesium sulfate.The diffusion of sulfate ions into concrete is a gradual process.In the early stages of corrosion,sulfate ion content in the concrete immersed in the magnesium sulfate solution is slightly less than that of the concrete immersed in the sodium sulfate solution.However,in the later stage of corrosion,the sulfate ion content in the concrete immersed in the magnesium sulfate solution is significantly higher than that of the concrete immersed in the sodium sulfate solution.

Effect of Alkaline Electrolyzed Water on Performance Improvement of Green Concrete with High Volume of Mineral Admixtures

The strength and durability of concrete will be significantly reduced at high volume of mineral admixture,and the poor early strength of concrete also still needs to be solved.In this investigation,a highly active alkaline electrolyzed waters was used as mixing water to improve the early strength and enhance the durability of green concrete with high volume mineral admixture,the influences of alkaline electrolyzed water(AEW)on hydration activity of mineral admixture and durability of concrete were determined.The results showed that compared with natural tap water,AEW can accelerate early hydration process of cement in concrete and produce comparatively more hydrated products,leading to a 13.6%higher compressive strength than that of ordinary concrete at early age,but the improvement effect of AEW concrete was relatively reduced at long-term age.Meanwhile,the activity of mineral admixtures could be stimulated by AEW to some extent,the strength and durability performance of AEW concrete after double doping 25%slag and 25%fly ash can still reach the level of ordinary cement concrete without mineral admixtures.The SEM micromorphology of 7 d hydrated natural tap water cement paste was observed to be flaky and tabular,but the AEW cement pastes present obvious cluster and granulation phenomenon.The SEM microstructure of AEW concrete with mineral admixtures is more developed and denser than ordinary tap water concrete with mineral admixtures.Therefore,the AEW probably could realize the effective utilization of about 50%mineral admixture amount of concrete without strength loss,the cement production cost and associated CO_(2) emission reduced,which has a good economic and environmental benefit.

Preparation and Dynamic Tensile Behavior of C200 Green Reactive Powder Concrete

A new type of green reactive powder concrete (GRPC) with compressive strength of 200 MPa is prepared by utilizing composite mineral admixtures, natural fine aggregates, and short and fine steel fibers. The quasi-static mechanical properties (mechanical strength, toughness, fracture energy and interfacial bonding strength) of GRPC specimens, cured in three different types of regimes, are investigated. The experimental results show that the mechanical properties of the C200 GRPC made with the powder binders that is composed of 40% of Portland cement, 25% of ultra fine slag, 25% of ultra fine fly ash and 10% of silica fume are better than the others'. The corresponding compressive strength, flexural strength and fracture energy are more than 200 MPa, and 30 000 J/ m2 respectively. The dynamic tensile behavior of the C200 GRPC is also investigated through the split Hopkinson pressure bar (SHPB) according to the spalling phenomenon. The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of GRPC. With the increase of strain rate, its peak stress and relevant strain increase. The GRPC exhibits an excellent strain ratio stiffening effect under the dynamic tensile load with high strain ratio, resulting in a significant change of the fracture pattern.

Anti-chloride permeability and anti-chloride corrodibility of a green high performance concrete admixture in concrete

The effects of green high performance concrete (GHPC) admixture on the anti-chloride permeability and anti- chloride corrodibility of concrete are studied by a series of experiments designed on the basis of the diffusion principle and electro-chemical principle. The GHPC admixture consists of fly ash, gangue, slag, red mud, etc., of which the mass fraction of industrial residues is over 96 %. The anti-permeabilities and anti-corrodibilities of the tested GHPC and normal concrete (NC) are evaluated by the Diffusion Coefficients of chloride which was obtained by measuring the concentration of chloride in the tested systems by the voltage difference method. It is found that the adoption of GHPC admixture greatly improves the anti-chloride permeability and anti-chloride corrodibility by modifying the inner structure and contracting the porosity of concrete to the reduce considerably the diffusion rate of chloride. The admixture is desirable regarding its engineering performances as well as economical and environmental interests.

Corrosion Performance of Stainless Steel Reinforcement in the Concrete Prepared with Seawater and Coral Waste and Its Ecological Effects

Durability and ecological effects of the stainless steel reinforced coral waste concrete were compared with those of the carbon steel reinforced ordinary concrete.The results showed that the corrosion current densities of the stainless steel in the coral waste concrete were less than one-tenth of those of the carbon steel in the same grade ordinary concrete.The stainless steel in the seawater coral waste concrete maintained passivation even after more than two years of immersion in 3.5%NaCl solution,while the carbon steel counterparts in the ordinary concrete were seriously corroded under the same condition.Simultaneously,the corrosion current density of the stainless steel reinforcement decreased slightly with the strength grade of the coral waste concrete.The ecological evaluation indicated that the non-renewable energy consumption and CO_(2)emission of per cubic meter of the newly constructed stainless steel reinforced coral waste concrete were 23.72%and 1.419%less than those of the carbon steel reinforced ordinary concrete with the same grade,while the aforementioned two parameters of the former material were reduced by 44.81%and 32.0%in comparison to the latter one in 50 years duration.

Partial Replacement of Cement by Solid Wastes as New Materials for Green Sustainable Construction Applications

The manufacturing of ordinary Portland cement is an energy-intensive process that results in pollution and CO2 emissions,among other issues.There is a need for an environmentally friendly green concrete substitute.Waste products from a variety of sectors can be recycled and used as a green concrete substitute.This decreases the environmental effects of concrete manufacturing as well as energy consumption.The use of solid waste materials for green building is extremely important now and in the future.Green concrete is also in its infancy in terms of manufacturing and application.Academics must intervene by encouraging business implementation.The aim of this review paper is to raise awareness about the importance of repurposing recycled materials and to highlight new technologies for producing green,sustainable concrete.