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.

INFLUENCE OF MINERAL ADMIXTURES ON MECHANICAL PROPERTIES OF HIGH-PERFORMANCE CONCRETE

The improvements of the mechanical properties, including bulk density of fresh mixtures, elastic modulus, and compressive strengths of four high-performance concrete mixtures, made with the addition of fly ash, refined ground blast - furnace microslag (microslag) and silica fume are studied. The concrete mixtures were determined based on the dispersion testing results. The study indicates that the elastic modulus at 28 and 91 days, and compressive strengths of the concretes are improved a lot when fly ash and microslag by 25 percent by weight of cement are added into the mixtures individually. The improvement is especially evident when silica fume by 5 percent and fly ash by 25 percent by weight of cement are added together into the mixture, while the fresh concrete mixture keeps a good workability. Through the analysis of chemically combined water ratios of the four mixtures at various hydration ages, it is found that the addition of all these mineral mixtures are beneficial to the hydration process, especially, at later stages, which might be one of the reasons for the improvement of mechanical properties. (Author abstract) 4 Refs.

Measurement and analysis of defects in high-performance concrete with three-dimensional micro-computer tomography

In order to investigate the effects of two mineral admixtures （i. e., fly ash and ground slag）on initial defects existing in concrete microstructures, a high-resolution X-ray micro-CT（ micro-focus computer tomography）is employed to quantitatively analyze the initial defects in four series of highperformance concrete （HPC）specimens with additions of different mineral admixtures. The nigh-resolution 3D images of microstructures and filtered defects are reconstructed by micro- CT software. The size distribution and volume fractions of initial defects are analyzed based on 3D and 2D micro-CT images. The analysis results are verified by experimental results of watersuction tests. The results show that the additions of mineral admixtures in concrete as cementitious materials greatly change the geometrical properties of the microstructures and the spatial features of defects by physical-chemistry actions of these mineral admixtures. This is the major cause of the differences between the mechanical behaviors of HPC with and without mineral admixtures when the water-to-binder ratio and the size distribution of aggregates are constant.

Grey Clustering Theory to Assess the Effect of Mineral Admixtures on the Cyclic Sulfate Resistance of Concrete

Concrete specimens made with ordinary portland cement or ordinary portland cement incorporating fly ash with the replacement of 10% or 20%, ground blast furnace slag with the replacement of 15% or 30%, or 15% fly ash and 15% ground blast furnace slag were made and exposed to a cyclic sulfate environment. Concrete properties including relative dynamic elastic modulus, chloride ion diffusion coefficient, compressive strength and flexural strength were measured. Effect of mineral admixtures on the cyclic sulfate resistance of concrete was assessed based on the grey clustering theory. The experimental results indicate that the cyclic sulfate resistance of concrete incorporating ground blast furnace slag belongs to the higher grey grade, which exhibits that it possesses excellent cyclic sulfate resistance. With increasing addition of fly ash, the cyclic sulfate resistance of concrete changes from the medium grey grade to the lower grey grade, which shows that incorporation of fly ash is disadvantageous for the cyclic sulfate resistance of concrete.

Properties and Microstructure of Marine Concrete with Composite Mineral Admixture

The influences of compositing mineral admixtures on the regularity of mechanical property, workability, durability and microstructure of C50 marine concrete were investigated. The results show that the incorporation of mineral admixtures can improve the mechanical properties and workability of C50 marine concrete, 3 min-doped mineral admixture had excellent resistance to chloride ion permeability. The microscopic structure mixing mineral admixtures system was well-distributed and compact, little macroporeare can be found.

Influence of Mineral Admixtures on Chloride Ion Permeation through Concrete

Through the rapid chloride ion penetration test,the influence of fly ash and slag on chloride ion permeability and microstructure of concrete was studied.The results indicate that the addition of fly ash increases concrete permeability at 28 days.With the slag content of 20% and 30%,the permeability of concrete at 28 days is reduced.The positive effect of slag is due to its relatively stronger pozzolanic reactive ability resulted in the most probable pore size and total porosity decreased.When the slag content reaches 40%,the concrete permeability showes the tendency ofincrease.

Influence of Mineral Admixtures on Corrosion of Steel Rebar in Concrete

The effects of several mineral admixtures such as silica fume,granulated ground blast furnace slag and fly ash at different replacement ratio instead of Portland cement on the corrosion of steel reinforced concrete were investigated.By measuring the rebar anode polarization curve,permeability of concrete,mass loss of steel rebar and the amount of chloride ions and hydroxide in mortar,the corrosion resistance of steel embedded in fresh mortar incorporated of salt and different mineral admixtures were evaluated respectively.The results show that most mineral admixture can not improve corrosion resistance of concrete at early ages.However,in the long term the addition of mineral admixtures can decrease obviously the permeability of concrete and free chloride content in the pore solution of concrete as well as effectively improve the protection ability of passive film of steel rebar.

Carbonation Resistance of Sulphoaluminate Cement-based High Performance Concrete

The influences of water/cement ratio and admixtures on carbonation resistance of sulphoaluminate cement-based high performance concrete （HPC） were investigated. The experimental results show that with the decreasing water/cement ratio, the carbonation depth of sulphoaluminate cement-based HPC is decreased remarkably, and the carbonation resistance capability is also improved with the adding admixtures. The morphologies and structure characteristics of sulphoaluminate cement hydration products before and after carbonation were analyzed using SEM and XRD. The analysis results reveal that the main hydration product of sulphoaluminate cement, that is ettringite （AFt）, decomposes after carbonation.

Performances of the High Strength Low Heat Pump Concrete (HLPC)

The effects of mineral admixtures on fluidity,mechanical and hydrational exothermic behavior were studied.The results show that,double adding ways,i e,fly ash and slag were added at the same time,not only improves the fluidity of fresh concrete with low W/B and compensates the lower early compressive strength of harden concrete caused by high adding amount of fly ash, but also greatly reduces the highest temperature rise, exothermic rate and total heat liberation of 3 day of binder pastes in HLPC, and postponed the arrival time of the highest temperature rise. HLPC was prepared and applied to project practice successfully.

The Corrosion Fatigue Properties of High Performance Concrete

With the loading test equipment of corrosion fatigue specially designed, the corrosion fatigue characteristics of high performance concrete (HPC) withstanding the interaction of third point fatigue loading and Na_2SO_4 solution were investigated and analyzed. The experimental results indicate that water-binder ratio evidently influences the corrosion fatigue characteristics of HPC, and a moderate quantitative fine mineral admixture enhances the corrosion fatigue resistance of HPC. The effect is more significant when fly ash and silica fume are added.

Evaluation of Sub-microstructure in Concrete with Low Water-binder Ratio by SEM-BSE Image Analysis

The coarse pore system, interfacial transition zone （ITZ） between aggregate and paste matrix and volume fraction of unhydrated cement in concrete （w/c=0.3） containing mineral admixtures were quantitatively characterized by the scanning electron microscope-backscattered electron （SEM-BSE） image analysis technique. The experimental results show that compound addition of slag and fly ash decreases the coarse porosity from 10.17% to 3.74% and the threshold diameter of coarse pore size from 345 μm to 105 μm compared with concrete （w/c=0.30） without mineral admixtures; Moreover with compound addition of fly ash and slag, the volume proportion of unhydrated cement in paste matrix is reduced by 30%, the maximum amount of coarse pores in the ITZ between aggregate and paste decreases from 13.11% to 5.57% and the thickness of ITZ is reduced by 37% , compared with concrete without mineral admixtures.

A Survey of High Performance Concrete Developments in Civil Engineering Field

High Performance concrete (HPC) has received increased attention in the development of infrastructure Viz., Buildings, Industrial Structures, Hydraulic Structures, Bridges and Highways etc. leading to utilization of large quantity of concrete. This paper presents a comprehensive coverage of High Performance concrete developments in civil engineering field. It highlights the High Performance concrete features and requirements over conventional concrete. Furthermore, recent trends with regard to High Performance Concrete development in this area are explored. This paper also includes effect of Mineral and Chemical Admixtures used to improve performance of concrete.

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.

Influence of shrinkage-reducing admixture on drying shrinkage and mechanical properties of high-performance concrete

High-performance concrete （HPC） has specific performance advantages over conventional concrete in strength and durability. HPC mixtures are usually produced with water/binder mass ratios （mW/mB） in the range of 0.2-0.4, so volume changes of concrete as a result of drying, chemical reactions, and temperature change cannot be avoided. For these reasons, shrinkage and cracking are frequent phenomena. It is necessary to add some types of admixture for reduction of shrinkage and cracking of HPC. This study used a shrinkage-reducing admixture （SRA） for that purpose. Concrete was prepared with two different mW/mB （0.22 and 0.40） and four different mass fractions of SRA to binder （w（SRA） = 0%, 1%, 2%, and 4%）. The mineral admixtures used for concrete mixes were： 25% fly ash （FA） and 25% slag by mass of binder for the mixture with mW/mB = 0.40, and 15% silica fume （SF） and 25% FA for the mixture with mW/mB = 0.22. Tests were conducted on 24 prismatic specimens, and shrinkage strains were measured through 120 days of drying. Compressive strength, splitting strength, and static modulus of elasticity were also determined. The results show that the SRA effectively reduces some mechanical properties of HPC. The reductions in compressive strength, splitting tensile strength, and elastic modulus of the concrete were 7%-24%, 9%-19%, and 5%-12%, respectively, after 90 days, compared to concrete mixtures without SRA. SRA can also help reduce drying shrinkage of concrete. The shrinkage strains of HPC with SRA were only as high as 41% of the average free shrinkage of concrete without SRA after 120 days of drying.

Effects of Curing Conditions on Strength Development of High Strength Concrete

This paper presents the results of a series of studies on the influence of curing conditions on the strength development of high strength concrete. The 1-, 3-, 7-, 14- and 28-day strengths of four different mixes of Grade 75 similar to 80 concrete, with or without pulverized fuel ash and/or condensed silica fume, under five different curing regimes were investigated. It is revealed that the curing conditions have significant influence on both the short term and long term strength development of the concrete and that concrete mixes of the same grade but containing different mineral admixtures show distinct favour for a curing regime. These results will be helpful for evaluating suitable curing methods for high strength concrete with different mix proportions.

MODIFICATION THE CEMENTIOUS MATERIAL OF ULTRA-HIGH-STRENGTH SLEEPER CONCRETE

This paper presents investigation results on the natural ultra-fine mineral flour of crystalline silica fume (CSF) and porous quartz sand stone (PQSS) which can modify cement mortar strength under hydrothermal synthesis reaction (HSR) in the autoclave-cured condition. The replacement of cement by CSF and PQSS can signifi cantly increase the Jflerural and compressive strength which reach 22MPa and 150MPa respectively and de-crease the porosity oj the cement mortar. The ratio oj fine aggregation, standard sand to cementions material has sig nificant influence on the mortar strength. The mechanisms involved in cement and natural mineral flour and the HSR are presented. CaO/SiO2 ratio ranges from 3. 20 to 1. 11. the main hydrate phase is C2SH and there is not Tober-morite through X-Ray diffraction qualitative analysis. The new and ultra-high strength cementious material as basic material of sleeper concrete can he used in prestressed reinforcement sleeper concrete.

STRENGTH EFFECT OF F MINERAL ADMIXTURE ON CEMENT CONCRETE

F mineral admixture (FMA) is made of the fin- ely divided powder of natural zeolite with a bit of other agent. When FMA is used to displace about 10% (by weight) of the ordinary portland cement (OPC) (strength grade 575#) in concrete and mixed with a suitable amount of super plasticizer (w/c =0.31-0.35), then a high-strength concrete with compressive strength about 80 MPa and slump about 180 MM can be obtained. The strength of this concrete is about 10-15% higher than that of the corresponding concrete mixing with pure OPC, and its bleeding decreases greatly. It makes no segre- gation and separation, and thus it satisfies the requirement of pumping concrete in construction.

An Experimental Study of Self-Compacting Concrete Made with Filler from Construction and Demolition Waste

This study evaluated the influence of the Portland cement replacement by 0, 5%, 10%, 15% and 20% of Construction and Demolition Waste (CDW) filler contents in the production of self-compacting concrete (SCC). The SCC mixtures were evaluated on fresh state by slump flow, J-ring, resistance of segregation, specific gravity, and on hardened state by compressive and splitting tensile strength, specific gravity, air voids and absorption rate. The results indicated that all SCC produced with CDW filler met the limits established at any level of substitution without changes of the w/c ratio or superplasticizer content. It was possible to verify that the presence of CDW filler, in substitution of cement, by volume, improves the resistance to segregation and up to 5% of CDW filler decreases the loss of fluidity with time as compared to reference. It was found that all SCC mixtures, at 28 days, had the average compressive strength above 50 MPa, without showing significant loss with up to 20% of CDW filler. For splitting tensile strength, SCC recycled mixtures reached up to 92.5% of the SCC used as reference. Absorption rate and air voids index of SCC recycled mixtures had a maximum increase of 1.60%Compared to the reference one. So, it is possible to conclude that the use of the CDW filler up to 20% in substitution of cement, by volume, is feasible for SCC production.

基于正交试验的再生透水混凝土路用性能研究

通过正交试验研究了粉煤灰、矿渣微粉、硅灰等矿物掺合料以及再生骨料替代率对再生透水混凝土抗压强度、有效孔隙率、透水系数、耐磨性的影响。结果表明:再生骨料替代率对再生透水混凝土28 d抗压强度和透水系数影响最显著,随再生骨料替代率的增加,28 d抗压强度逐渐降低,透水系数显著增大;粉煤灰掺量对磨坑长度的影响最显著,随粉煤灰掺量的增加,再生骨料透水混凝土的耐磨性显著提高。基于功效系数法,综合性能最优配比为:粉煤灰、矿渣微粉、硅灰掺量分别为15%、5%、8%,再生骨料替代率为30%,制得的再生透水混凝土28 d抗压强度为25.9 MPa,透水系数为2.04 mm/s,磨坑长度为31.7 mm。

高岩温环境下矿物掺合料对喷射混凝土强度和抗渗性的影响

针对高岩温隧道环境下喷射混凝土出现后期强度下降及耐久性劣化等问题,研究了80℃干热养护条件下不同矿物掺合料(粉煤灰、矿粉、硅灰)在单掺以及二元、三元复掺情况下对喷射混凝土长期强度稳定性、抗水渗透性能和抗氯离子渗透性能的影响,并通过分析硬化混凝土气泡结构参数揭示其提升机理。结果表明:单掺5%硅灰或复掺10%矿粉+5%硅灰可以明显改善喷射混凝土的长期强度稳定性及抗渗性,56 d抗压强度无倒缩,渗水高度分别降低至78、101 mm。三元复掺体系(10%粉煤灰+10%矿粉+5%硅灰)喷射混凝土的抗氯离子渗透性能最佳,其28、56 d氯离子扩散系数分别降低至6.4×10^(-12)、13.0×10^(-12)m^(2)/s。