Effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete

The effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete （SCGC） was investigated in this paper. The work focused on the concrete mixes with a fixed water-to-geopolymer solid （W/Gs） ratio of 0.33 by mass and a constant total binder content of 400 kg/m3. The mass fractions of silica fume that replaced fly ash in this research were 0wt%, 5wt%, 10wt%, and 15wt%. The workability-related fresh properties of SCGC were assessed through slump flow, V-funnel, and L-box test methods. Hardened concrete tests were limited to compressive, splitting tensile and flexural strengths, all of which were measured at the age of 1, 7, and 28 d after 48-h oven curing. The results indicate that the addition of silica fume as a partial replacement of fly ash results in the loss of workability; nevertheless, the mechanical properties of hardened SCGC are significantly improved by incorporating silica fume, especially up to 10wt%. Applying this percentage of silica fume results in 4.3% reduction in the slump flow; however, it increases the compressive strength by 6.9%, tensile strength by 12.8% and flexural strength by 11.5%.

Recycled Aggregates:Production,Properties and Value-added Sustainable Applications

Part of an extensive research undertaken by the Concrete and Masonry Research Group at Kingston University-London was reported to demonstrate through scientific research and full-scale site trials,that quality recycled concrete aggregates can be produced and can be used successfully in a range of concrete applications.The effects of up to 100% coarse recycled concrete aggregate（RCA） on fresh,engineering and durability related properties were established and assessed its suitability for use in a rage of sustainable applications.

Production and Properties of Superplasticized Concrete

The objective of this research is to study the effect of grinding powdered superplasticizer, Portland cement, sand, and silica fume on the properties of fresh and hardened concrete. Lose Angeles Machine was used to grind these constituents. The program was arranged to determine the effect of cycles＇ number, superplasticizer type and dosage, silica fume dosage and condition, and gravel to sand ratio on properties of concrete. Naphthalene sulphonated formaldehyde （NSF） superplasticizers in the forms of liquid and powdered were used. Silica fume may be grinded with the other constituents （grinded）, or added to concrete mixer （normal）. The water/cement （w/c） ratio varied from 0.35 to 0.55 to achieve a constant slump （50-90 mm）. Slumps, bulk density and mechanical properties of concrete were measured. Scanning electron microscope （SEM） was also used to show the differences between traditional and superplasticized concrete. The results showed that grinding the mixture enhances fresh and hardened concrete properties. It is also observed that grinding the mixture for 500 cycles is more effective than other numbers of grinding. In addition, superplasticized concrete exhibits compressive strength higher than traditional one at varied ages. Moreover, using powdered superplasticizer has a remarkable effect on enhancing concrete properties rather than using it in a liquid form. A dosage of 1% by weight of cement gave the highest results of compressive strength. Silica fume has an essential role in improving concrete strength and durability since it acts as very efficient void filler and as a super pozzolana. SEM observations illustrate that grinding the mixture enhances transition zone （TZ） properties and makes it denser. On the other hand, grinded mixture can be packaged in bags and transported for use in crowded cities, and so, enhances quality control, since the only requirement to obtain superplasticized concrete is to add water and gravel. This technique has many benefits such as; saving cement, labor and noise, high quality control, and enhancing concrete permeability and durability. There are many fields of application of superplasticized concrete such as; in locations which are not easily accessible by ordinary concreting techniques, in repairing and strengthen, thin coating, and for small projects when ready mix supply is not feasible.

Influences of fiber length and water film thickness on fresh properties of basalt fiber-reinforced mortar

In plain mortar,the water film thickness(WFT)has been found to play a key role in the fresh properties.However,in fiber-reinforced mortar,the role of WFT has not been investigated yet.In this research,basalt fibers of different lengths were added to the mortar,and the dynamic and static flowability,cohesiveness,adhesiveness,and packing density were tested to study the effects of fiber length on the packing density and WFT,and the combined effects of fiber length and WFT on the fresh properties.The results showed that in fiber-reinforced mortar,the WFT also plays a key role,whereas the fiber length exerts its influences through the indirect effects on the packing density and WFT and the direct effect on fiber-mortar interaction.Basically,an increase in fiber length decreases the packing density and WFT,decreases the dynamic and static flowability needed for placing,increases the cohesiveness needed for avoiding segregation,and,quite unexpectedly,decreases the adhesiveness needed for rendering and spraying applications.Regression analysis yielded good correlation of the fresh properties to fiber length and WFT,and best-fit formulas for the mix design for basalt fiber-reinforced mortar were obtained.

An experimental study for optimization of high range water reducing superplasticizer in self compacting concrete

Concrete is extensively used construction material in the infrastructure development industry.With increase in technical knowhow,the need of research for high performance concretes such as self-compacting concrete(SCC)has increased in the last decade.The adaptability of SCC is due to its fluidic behavior in fresh state.However,to develop SCC using indigenous materials,the lack of standardized mix design procedures is the biggest impediment.Although with the advent of chemical admixtures,it is possible to achieve concrete with high fluidity,but at the same time durability issues require more attention.To have these fresh state properties SCC mixes are typically designed with high powder contents,and chemical admixtures.Proportioning and optimization of these materials is a key issue in the mix design of SCC.This paper focuses mainly on experimental study to optimize dosages of superplasticizer for mortar of SCC and then in concrete mixture itself.

Recycled glass replacement as fine aggregate in self-compacting concrete

With increasing environmental pressure to reduce solid waste and to recycle as much as possible,the concrete industry has adopted a number of methods to achieve this goal by replacement of waste glass with concrete composition materials.Due to differences in mixture design,placement and consolidation techniques,the strength and durability of Self Compacting Concrete(SCC)may be different than those of conventional concrete.Therefore,replacement of waste glass with fine aggregate in SCC should deeply be investigated compared to conventional concretes.The aim of the present study is to investigate the effect of glass replacement with fine aggregate on the SCC properties.In present study,fine aggregate has been replaced with waste glass in six different weight ratios ranging from 0%to 50%.Fresh results indicate that the flow-ability characteristics have been increased as the waste glass incorporated to paste volume.Nevertheless,compressive,flexural and splitting strengths of concrete containing waste glass have been shown to decrease when the content of waste glass is increased.The strength reduction of concrete in different glass replacement ratios is not remarkable,thus it can be produced SCC with waste glass as fine aggregate in a standard manner.

Optimization of Strength Properties of Reactive Powder Concrete by Response Surface Methodology

The main objective of this study is to optimize the fresh and strength properties of reactive powder concrete incorporated with industrial by-products like ultra-fine ground granulated blast furnace slag as cement substitute and added with coal bottom ash and recycled concrete fines as partial replacement of quartz sand by response surface methodology through design of experiment approach.Totally four responses namely slump,compressive strength(C-28),flexural strength(F-28),and split-tensile strength(S-28)after 28 days of curing period were considered.The statistical study on the reactive powder concrete includes the modeling of regression,normal probability plots,surface plot analysis,and optimization of process variables.The regression models of the considered responses(slump,C-28,F-28,and S-28)were tested.The results obtained from the analysis of variance(ANOVA)and Pareto chart were used to determine the statistical significance of the process variables.The influence of the variables on the responses was studied by means of the surface plot analysis.The optimal proportion of the variables against the responses was obtained through optimization response.The resulted regression equations were in the form of second-order polynomial equation and the prediction of strength properties was found to be in line with the experimental results.The difference of proportion of variance indicated that only 0.43%,6.42%,5.15%,and 9.7%of deviations cannot be expressed by the analysis.The ANOVA and Pareto charts represented the high significance and appropriateness of the linear term of slump response and the two-way interaction term of strength responses.The results of the optimization response revealed the optimal proportions of recycled concrete fines and coal bottom ash as 19.15%and 7.02%,respectively.