Effect of Limestone Powder and Fly Ash on Magnesium Sulfate Resistance of Mortar

The effect of limestone powder and fly ash on magnesium sulfate resistance of mortar was studied by testing on the strength, expansion and hydration products of the specimens stored in MgSO4 solution at certain periods. The experimental results show that the strength of mortar stored in MgSO4 solution increases a little before 28 d, but decreases fast subsequently. The more the contents of limestone powder and fly ash, the less the strength losses. Mortar swells in the MgSO4 solution with the soaking time. And the more the contents of limestone powder and fly ash, the less the expansion rate is. The expansion or strength loss of mortars results from the expansion of gypsum, as well as the loss of Ca（OH）2 and other hydration products of cement. The magnesium sulfate resistance of the mortars containing limestone powder and fly ash is high.

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.

SULFATE RESISTANCE MECHANISM OF HIGH- PERFORMANCE CONCRETE CONTAINING NCI

It is found that the incorporation of Nitrite Corrosion Inhibitor (NCI) greatly weakens the resistance of mixtures to sulfate attack. To study the mechanism of this phenomenon, in this paper, the influence of NCI addition on the cement paste and microstructure change of high performance concrete specimens is studied by means of quantitative XRD, SEM tests. The results demonstrate that the incorporation of NCI accelerates the formation of calcium hydroxide and ettringite crystals, and weakens the pore refinement effect caused by the secondary hydration reaction of fly ash and microsilica. At the age up to one year, the relative crystal quantity in mixture containing NCI is always higher than that in control mixture. The reasons for the degradation in sulfate resistance of mixtures may be attributed to the increase and stability of the calcium hydroxide and ettringite crystals formed and the weakening of secondary hydration reaction. Based on the results, conclusion can be drawn that NCI should be used cautiously in practical engineering where high resistance to sulfate attack is required. (Author abstract) 7 Refs.

Study on the Durability of Recycled Powder Concrete against Sulfate Attack under Partial Immersion Condition

In order to make full use of waste recycled fine powder(RFP)in concrete and achieve the goal of carbon neutrality in the concrete industry,the durability of sulfate resistance is an important aspect of evaluating the performance of recycled powder concrete(RPC).Therefore,the durability of RPC under partial sulfate immersion was studied to provide theoretical guidance for understanding the erosion mechanism of RPC.The compressive strength,mass loss,and microstructure change patterns of RPC under partial immersion of 5%Na2SO4 and MgSO4 solutions were analyzed by cubic compressive strength,mass loss rate,SEM-EDS,and XRD.The results showed that the surface crystalline matter of concrete in Na2SO4 solution was mainly white powders,and that of concrete in MgSO4 solution was mainly transparent paste,both of which had a little spalling on the outer surface of the concrete.The compressive strength and mass loss rate of concrete with 20%RFP was relatively good,indicating that concrete with 20%RFP had better durability against sulfate.The compressive strength of the lower part of the concrete partially immersed in Na2SO4 solution was higher than that of the upper part and the strength of the lower part of RPC-2 was 3.11%higher than the upper part at 180 d;The pattern was reversed in the MgSO4 solution,where the strength of the lower part of RPC-2 was 19.74%lower than the upper part at 180 d.Microscopic analysis showed that the hydration products of RPC were mainly gypsum and ettringite,while the RPC produced more hydration products with the promotion of magnesium ion in the MgSO4 solution.The higher the replacement rate of RFP,the more frequent the gypsum-type failures in the concrete.

Significance of compaction time delay on compaction and strength characteristics of sulfate resistant cement-treated expansive soil

The addition of cement for stabilization of expansive soils is one of the most commonly used methods.As with every calcium-based stabilizer,the time delay between the physical mixing of the stabilizer and compaction plays an important role in achieving the desired results after stabilization.However,a clear insight on the determination of optimum time delay for achieving the maximum desired compaction properties of cement-stabilized soils is yet to be established.Furthermore,the recent studies highlighted the use of sulfate to mitigate the negative effect of compaction time delay.The only drawback with the use of sulfate along with calcium-based stabilizers is the formation of ettringite,which deteriorates the stabilized soil matrix.In view of this,the present study is aimed at using the sulfate resistant cement(SRC)as a stabilizer along with the controlled addition of sulfate solutions to mitigate the negative effect of compaction time delay in stabilizing the expansive soil.To bring out the above effects,three periods of time delays(0 h,6 h and 24 h)and three sulfate concentrations of 5000 parts per million(ppm),10,000 ppm and 20,000 ppm were adopted.The experimental results showed that the delay in compaction resulted in the formation of clogs and reduction of strength of SRC-stabilized expansive soil.Upon sulfate addition to SRC-stabilized expansive soil,the formation clogs was not curtailed and resulted in the formation of ettringite clusters.These formations were captured with the help of scanning electron microscope(SEM)images and validated with electron dispersive X-ray spectroscopy(EDAX)analysis.Further,an attempt is also made to explain the mechanism of density and strength reduction with the aid of physico-chemical properties and mercury intrusion porosimetry(MIP)studies.

Effect of Aggregate Gradation with Fuller Distribution on Properties of Sulphoaluminate Cement Concrete

Experimental investigations on mechanical property and durability of sulphoaluminate cement concrete with aggregate gradations according to Fuller distribution are presented in this paper. Compressive strength, water impermeability and resistance capability to sulfate attack of SACC have the same trend of concrete with fine aggregates of Fuller distribution gradation<concrete with coarse aggregates of Fuller distribution gradation<concrete with total aggregates of Fuller distribution gradation. The relationship between bulk density of aggregate and water penetration depth obeyed the second-order polynomial y=0.002x2-6.863 8x +5 862.3, and had a notable correlation R2=0.979 9. The sulphoaluminate cement concrete with total aggregate gradation with Fuller distribution for h=0.50 had the best resistance capability to sulfate attack. It was a second-order polynomial relationship between bulk density of aggregates and water penetration depth of y=0.002x2-6.863 8x+5 862.3 with R2=0.979 9, which indicated notable correlation. The fitting formula between bulk density of aggregates and sulfate resistance coefficient of SACC was y=0.000 5x+0.370 4 with R2=0.958 5.

Effects of natural zeolite and sulfate ions on the mechanical properties and microstructure of plastic concrete

One of the strategic materials used in earth-fill embankment dams and in modifying and preventing groundwater flow is plastic concrete(PIC).PIC is comprised of aggregates,water,cement,and bentonite.Natural zeolite(NZ)is a relatively abundant mineral resource and in this research,the microstructure,unconfined strength,triaxial behavior,and permeability of PIC made with 0%,10%,15%,20%,and 25% replacement of cement by NZ were studied.Specimens of PIC-NZ were subjected to confined conditions and three different confining pressures of 200,350,and 500 kPa were used to investigate their mechanical behavior and permeability.To study the effect of sulfate ions on the properties of PIC-NZ specimens,the specimens were cured in one of two different environments:normal condition and in the presence of sulfate ions.Results showed that increasing the zeolite content decreases the unconfined strength,elastic modulus,and peak strength of PIC-NZ specimens at the early ages of curing.However,at the later ages,increasing the zeolite content increases unconfined strength as well as the peak strength and elastic modulus.Specimens cured in the presence of sulfate ions indicated lower permeability,higher unconfined strength,elastic modulus,and peak strength due to having lower porosity.

Enhancing compressive strength and durability of self-compacting concrete modified with controlled-burnt sugarcane bagasse ash-blended cements

In sugar industries,the growing amount of sugarcane bagasse ash(SBA),a byproduct released after burning bagasse for producing electricity,is currently causing environmental pollution.The residual ash displays a pozzolanic potential;and hence,it has potential as a cement addictive.This study focuses on enhancing suitability of SBA through incorporating ground blast furnace slag(BFS)in manufacturing self-compacting concretes(SCCs).For this purpose,SBA was processed by burning at 700°C for 1 h,before being ground to the cement fineness of 4010 cm2/g.SCC mixtures were prepared by changing the proportions of SBA and BFS(i.e.,10%,20%,and 30%)in blended systems;and their performance was investigated.Test results showed that the presence of amorphous silica was detected for the processed SBA,revealing that the strength activity index was above 80%.The compressive strength of SCC containing SBA(without BFS)could reach 98%–127%of that of the control;combination of SBA and 30%BFS gets a similar strength to the control after 28 d.Regarding durability,the 10%SBA+30%BFS mix exhibited the lowest risk of corrosion.Moreover,the joint use of SBA and BFS enhanced significantly the SCC’s sulfate resistance.Finally,a hyperbolic formula for interpolating the compressive strength of the SBA-based SCC was proposed and validated with error range estimated within±10%.

Effects of SO2 on the low temperature selective catalytic reduction of NO by NH3 over CeO2-V2O5-WO3/TiO2 catalysts

The CeO2-V2O5-WO3/TiO2 （CeO2-VWT） catalysts were prepared by one-step and two-step impregnation methods. The effects of different loading of CeO2 and different preparation methods on De-NOx activity of catalysts had been investigated. CeO2 helped to improve the De-NOx activity and sulfur resistance. The optimal loading of CeO2 was 3% with the De-NOx efficiency reached 89.9% at 140℃. The results showed that the De-NOx activity of 3% CeO2-VWT catalysts by one-step method was the same as two-step method basically and reached the level of industrial applications, the N2 selectivity of catalysts was more than 99.2% between 110℃ and 320℃. In addition, CeO2 promoted the oxidation of NO to NO2, which adsorbed on the Lewis acid site （V5＋-O） to form V5＋-NO3 and inspired the fast SCR reaction. Not only the thermal stability but also the De-NOx activity of catalysts decreased with excess CeO2 competed with V2O5. Characterizations of catalysts were carried out by XRF, BET, XRD, TG and FT-IR. BET showed that the specific surface area of catalysts decreased with the loading of CeO2 increased, the active components content and specific surface area of catalysts decreased slightly after entering SO2. Ammonium sulfate species were formed in poisoned catalyst which had been investigated by XRF, BET, TG and FT-IR. The largest loss rate of weight fraction was 0.024%.℃-1 at 380℃ 390℃, which was in accordance with the decomposition temperature of NH4HSO4 and （NH4）2SO4,