Limestone addition effects on concrete porosity

The effect on porosity (including absorption and sorpitivity) of cement paste and mortar/concrete, of limestone addition to Portland cement is assessed. Based on globally sourced literature published in English since 1993, consisting of 171 publications from 35 countries. The data analysed were from wide ranging tests. The effect on pore structure was also examined in terms of type of Portland cement and limestone, cement fineness and method of producing it, curing, maturity and water-cement ratio, as well as the cement composites with fly ash, slag (GGBS), silica fume and metakaolin and related to strength. Overall, it is suggested that though the use of limestone up to 25% with Portland cement should not impair the pore structure, limit on limestone content for its effect on strength is likely to be about 15%. This should be considered where higher proportion of limestone content is allowed in the Standards.     

Mechanical properties and durability of mortar and concrete containing natural pozzolana and limestone blended cements

The benefits of limestone filler (LF) and natural pozzolana (NP) as partial replacement of Portland cement are well established. Economic and environmental advantages by reducing CO₂ emission are well known. However, both supplementary materials have certain shortfalls. LF addition to Portland cement causes an increase of hydration at early ages inducing a high early strength, but it can reduce the later strength due to the dilution effect. On the other hand, NP contributes to hydration after 28 days improving the strength at medium and later ages. Hence, ternary blended cement (OPC–LF–NP) with better performance could be produced. In this paper, mortar prisms in which Portland cement was replaced by up to 20%LF and 30%NP were tested in flexure and compressive strength at 2, 7, 28 and 90 days. Some samples were tested under sulfate and acid solutions and for chloride ions permeability. Results show that the use of ternary blended cement improves the early age and the long-term compressive and flexural strengths. Durability was also enhanced as better sulfate, acid and chloride ions penetration resistances were proved.     

Improvement of the early-age reactivity of fly ash and blast furnace slag cementitious systems using limestone filler

This article analyzes the effects of the addition of limestone filler on the hydration rate, setting times and early-age mechanical properties of binary and ternary-binder mortars containing Portland cement, blast furnace slag (BFS) and fly ash (FA), with various substitution rates of cement with mineral additions going up to 50%. Vicat needle penetration tests and measurements of heat flow of reaction, compressive strength and dynamic Young’s modulus were carried out on 14 mortars prepared with binary and ternary binders, at 20°C. The results obtained on the mortars containing binary binders, show that their loss of mechanical strength at early age is not caused by a deceleration of the reactions of cement in the presence of mineral additions, but is mainly explained by the dilution effect related to the reduction in cement content. A moderate addition of limestone filler (8–17%) makes it possible to obtain ternary binders with early-age reactivity equal or even higher than that of Portland cement, and with 28-days mechanical resistance close to those of the binary-binder mortars. This accelerating effect of limestone filler is particularly sensitive in the case of mortars containing FA.     

An analysis of the properties of Portland limestone cements and concrete

In this paper the main factors affecting the properties of Portland limestone cements are discussed while the hydration behavior of limestone cements is examined. In addition, the intergrinding process, concerning the production of the limestone cements, is studied. Finally the properties and the behavior of limestone cement concrete as well as the corrosion behavior of limestone cement mortar are investigated. It is concluded that the fineness of clinker and limestone is strongly connected with the limestone content and the fineness of the cement. The limestone cements indicate satisfactory strength and generally demand less water than the relative pure cements. The limestone addition improves the clinker reactivity and the exploitation of its hydraulic potential. The Portland limestone cements indicate competitive concrete properties and improve the corrosion performance of the concrete.     

Compressive strength and drying shrinkage of fly ash-bottom ash-silica fume multi-blended cement mortars

This paper studies the physical properties, compressive strength and drying shrinkage of multi-blended cement under different curing methods. Fly ash, ground bottom ash and undensified silica fume were used to replace part of cement up to 50% by weight. Specimens were cured in air at ambient temperature, water at 25, 40 and 60 °C, sealed with plastic sheeting for 28 days. The results show that absorption and volume of permeable pore space (voids) of blended cement mortars at 28 day under all curing methods tend to increase with increasing silica fume replacement. The compressive strength of blended cement with fly ash and bottom ash was lower than that of Portland cement control at all curing condition while blended cement with silica fume shows higher compressive strength. In addition, the compressive strength of specimens cured with water increased with increasing curing temperature. The drying shrinkage of all blended cement mortar cured in air was lower than that of Portland cement control while the drying shrinkage of blended cement mortar containing silica fume, cured with plastic sealed and water at 25 °C was higher than Portland cement control due to pore refinement and high autogenous shrinkage. However, the drying shrinkage of blended cement mortar containing SF cured with water at 60 °C was lower than that of Portland cement control due to lower autogenous shrinkage and the reduced microporosity of C–S–H.     

Fine limestone additions to regulate setting in high volume fly ash mixtures

High volume fly ash (HVFA) concrete mixtures are being considered more frequently due to their cost and sustainability advantages. While the long term performance of these HVFA concretes typically meets or exceeds that of conventional concretes, their early age performance is often characterized by excessive retardation of the hydration reactions, delayed setting times, and low strengths. Extending an HVFA mixture to a ternary blend that incorporates a fine limestone powder may provide a viable solution to these deficiencies, particularly the hydration retardation and setting issues. In this paper, a nano-limestone powder and two other limestone fillers of increasing median particle size (4.4 μm and 16.4 μm) are investigated for their propensity to accelerate early age reactions and reduce setting times in a Class C fly ash/cement blend. The fineness of the limestone has measurable effects on its efficacy in accelerating hydration and decreasing setting times. Companion specimens prepared with a fine silica powder suggest that the fine limestone may act favorably through both a physical and a chemical mechanism. Isothermal calorimetry and Vicat needle penetration measurements on pastes are accompanied by strength measurements on mortars, to verify that the limestone powder substitutions are not negatively impacting strength development. A linear relationship with a reasonable correlation is found to exist between 1 d and 7 d compressive strengths of mortars and their accompanying cumulative heat release values as determined using isothermal calorimetry.     

富硅镁镍渣粉磨细度和掺量对硅酸盐水泥水化特性的影响

通过机械粉磨,将富硅镁镍渣(简称"镍渣")粉磨至微米级,制得的镍渣用作水泥混合材部分替代硅酸盐水泥熟料。测试并分析了镍渣的化学组成、细度、筛余量、体积安定性及孔结构。结果表明:4种镍渣的细度均大于硅酸盐水泥熟料,使得水泥颗粒密度随着镍渣掺量增加而减小;镍渣的胶凝活性低于硅酸盐水泥熟料,使得掺有镍渣的水泥粉末水化反应放热量降低,并伴随有缓凝现象,但随镍渣细度提高,有助于改善其反应活性;掺入镍渣不利于硬化水泥砂浆的抗压强度、抗折强度发挥,提高镍渣细度,则由于紧密堆积效应可改善力学性能;镍渣中的MgO不以f-MgO形式存在,使得硬化水泥浆体的体积安定性合格。     

Comparison of ground waste glass with other supplementary cementitious materials

Finely ground glass has pozzolanic properties that make attractive its recycling as supplementary cementitious material. This paper compares the behaviour of waste glass powders of different fineness with that of natural pozzolana, coal fly ash and silica fume. Chemical analysis, compressive strength measurements and durability tests were carried out to investigate the effect of ground glass on strength and durability performances of mortars. Blended both with Portland cement and lime, ground glass improved strength, resistance to chloride penetration and resistance to sulphate attack of mortars more than natural pozzolana and similarly to fly ash. Mortars with ground glass immersed in water for seven years did not show any sign of degradation and increased their compressive strength. The ranking of ground glass with respect to the other mineral additions was not affected by fineness.     

Simple methods to estimate the influence of limestone fillers on reaction and property evolution in cementitious materials

A commercial interest in sustainable cementing materials is driving efforts to reduce the use of cement in concrete. Limestone fillers are a promising direction towards achieving such cement use reductions. In spite of increasing filler use, little information is available to rapidly estimate the influences of limestone fillers, and more importantly filler fineness on reaction and property development. This work develops simple models to predict the effect of particle size classified limestone on hydration reactions and compressive strength development. The method builds on a relativistic basis, such that enhancements and alterations in reactions and properties are described in relation to a given control (pure cement) mixture. The prediction method considers aspects such as: (1) accelerations in reactions, (2) changes in inter-particle spacing as linked to the limestone filler’s fineness and (3) a porosity increase with increasing cement replacement. The predictive power of the approach is demonstrated for a variety of mixtures composed using three ASTM C150 compliant cements and forwards a basis for developing mixture proportioning strategies, such that apriori estimations of the mixture response (reaction rate and mechanical properties) can be used to optimize binder proportioning and thus strategize new methods to limit cement use in concrete construction applications.     

A study on hydration,compressive strength,and porosity of Portland-limestone cement mixes containing SCMs

In this study, the hydration of Portland-limestone cement (PLC) pastes and the relationship between compressive strength and porosity of PLC mortar samples containing various levels of supplementary cementitious materials were examined using XRD and MIP techniques. The results revealed that part of the limestone portion of Portland-limestone cements reacts with the alumina phases and produces carboaluminates, which increases compressive strength and reduces porosity. There is an optimum level of limestone corresponding to the available amount of alumina in the binder. Addition of slag or metakaolin provided more alumina, causing more limestone to participate in the hydration reaction and increasing the optimum level of limestone.     

Microstructural investigation of a silica fume–cement–lime mortar

Several additions, minerals and organic, are used in mortars, such as pozzolanic materials, cementicious materials and polymers. Literature about the use of additions in masonry mortars (cement/lime/sand mixes) is scarce; usually, studies are about concrete mortars. The purpose of this work is to study the microstructural effects of the substitution of 10% of Portland cement by silica fume in a 1:1:6 (cement/lime/sand mix proportion by volume) masonry mortar. Scanning electron microscopy with energy dispersive X-rays analysis (SEM/EDX) shows that, with silica fume, the C–S–H formed is type III at early ages and that type III and type I coexist at later ages. Silica fume lowers the total porosity and increases compressive strength only at later age and, as expected, the pore structure of mortar with silica fume is found to be finer than of non-silica fume mortar.     

Assessing the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste

This study assesses the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste. rice husk ash (RHA), palm oil fuel ash (POFA) and river sand (RS) were ground to obtain two finenesses: one was the same size as the cement, and the other was smaller than the cement. Type I Portland cement was replaced by RHA, POFA and RS at 0%, 10%, 20%, 30% and 40% by weight of binder. A water to binder ratio (W/B) of 0.35 was used for all blended cement paste mixes. The percentages of amorphous materials and the compressive strength of the pastes due to the hydration reaction, filler effect and pozzolanic reaction were investigated. The results showed that ground rice husk ash and ground palm oil fuel ash were composed of amorphous silica material. The compressive strength of the pastes due to the hydration reaction decreased with decreasing cement content. The compressive strength of the pastes due to the filler effect increased with increasing cement replacement. The compressive strengths of the pastes due to the pozzolanic reaction were nonlinear and were fit with nonlinear isotherms that increased with increasing fineness of RHA and POFA, cement replacement rate and age of the paste. In addition, the model that was proposed to predict the percentage compressive strength of the blended cement pastes on the basis of the age of the paste and the percentage replacement with biomass ash was in good agreement with the experimental results. The optimum replacement level of rice husk ash and palm oil fuel ash in pastes was 30% by weight of binder; this replacement percentage resulted in good compressive strengths.     

Portland cement-fly ash-silica fume systems in concrete

Laboratory flow, strength, and ultrasnic pulse velocity tests were performed on mortars made with 70% (by weight) of portland cement and 30% of pozzolanic materials where the pozzolanic materials consisted of various combinations of fly ash and silica fume. In addition to these ternary systems, binary blends, such as Portland cement and fly ash, and Portland cement and silica fume, along with 100% Portland cement mortars, were investigated for comparison. The purpose of the investigation, preliminary in nature, was to see under what circumstances, if any, would be a synergistic action when a ternary system of Portland cement-fly ash-silica fume is used in a mortar or concrete.Mortars were made with two cements of type I and two cements of type III along with class F and class C fly ashes. One silica fume was used. Standard flow tests were performed on the fresh mortars, and compressive strength as well as ultrasonic pulse velocity tests were performed with each hardened mortar at various ages up to 28 days. It is expected that the results and conclusions obtained here on mortars will be transferable to concretes.There are several novel, or at least lesser known, results of the investigation. For instance, a new explanation is offered for the plasticizing effect of fly ash which is based on the optimum particle-size distribution concept. Another such result is that ground fly ash produced greater flow increases with type I cement than with type III. A third finding is that the superplasticizer is more effective in increasing the flow as well as strength when the mortars contain fly ash and/or silica fume than in the case of mortars without mineral admixture. Also, it appears that when type I cement is used, the silica fume in the quantity of 5% of the weight of the cement produces relatively greater strength increase in the presence of fly ash than without fly ash.These promising results are preliminary in nature. Therefore, further research is justified with ternary systems in concrete. The presented work is a portion of a larger investigation.     

Rheological behaviour of ultra-high performance cementitious composites containing high amounts of silica fume

This study investigates the rheological behaviour of ultra-high performance cementitious composite mortars containing 15–25 % of silica fume. The utilization of two Portland cements with different mineralogical compositions and their influence on yield stress of mortar was monitored. The coaxial rheometer was used for determination of flow curves of tested samples. It was found that besides the relation between flow and water-to-binder ratio, there is also a substantial relationship with the mortar composition, in particular with the content of silica fume. The yield stress can be described by an exponential function of volume content of solids in the mortar. Such a function can describe not only the influence of granulometry but also the impact of structure formation on early age Portland cement hydration. It was found that the estimation of yield stress can be done even by a simple modular in-field technique such as a spread flow test.     

Simulation of the microstructure formation in hardening self-compacting cement paste containing limestone powder as filler via computer-based model

With the development of concrete technology, fillers are widely used in high performance concrete to improve its properties. Among them, limestone powder is popularly added in self-compacting concrete to gain good flowability. However, by lack of experimental data, several materials properties after the addition of limestone powder are still not sure, which actually yield some uncertainty for the further use of limestone powder in cement-based materials. In this study, by employing computer-based model, the microstructure of self-compacting cement paste containing limestone as filler is simulated and further used to investigate the role of limestone in hardening materials. To gain this goal, thermometric isothermal conduction calorimetry, thermal analysis and backscattered electron image acquisition were applied to understand the hydration kinetics with the addition of limestone filler. After that, a computational materials model based on HYMOSTRUC was developed to simulate the formation of microstructure in materials containing limestone powder. The predictive ability of the model was validated with the experimental test results. Then the developed model was employed to investigate the influence of several variables, such as water to cement ratio, limestone filler content and fineness, on the microstructure formation in hardening materials. The numerical experiments show that the addition of limestone filler could result in a denser microstructure at the initial hydration stage. With the proceeding of hydration, the limestone powder has a decreasing influence on the microstructure, and could obstruct somewhat the formation of a denser microstructure at later hydration stage. And it is found that computer-based modelling is an effective method to provide insights into the material behaviour, by relieving researchers from numerous repeated experiments.     

Portland-limestone cements. Their properties and hydration compared to those of other composite cements

The new European Standard EN 197-1 emphasizes the development of composite cements. In Greece a variety of pozzolanic and/or hydraulic materials are used as cement main constituents. Until now, limestone could be used only as a filler (up to 3% w/w), but since 2001 (application of EN 197-1) it can also be used as a main cement constituent. In this work a comparison between limestone and some of the materials that are already used in Greece is presented. An ordinary Portland cement and three Portland-composite cements containing limestone, natural pozzolana or fly ash were produced. The grinding process was designed in order to produce cements of the same 28 day compressive strength. The mechanical and physical properties of the cements were measured and hydrated products, formed after 1–28 days, were identified by means of XRD. The composite cements present significant differences as far as the clinker fineness, the development of the strength, the water demand and the hydration rate is concerned. The production of Portland-limestone cements seems to be very challenging, due to the satisfactory properties of the limestone cements as well as the low cost and the high availability of limestone in Greece.     

超细矿渣粉对硅酸盐水泥性能和微观结构的影响

通过掺入不同量的超细矿渣粉,研究其对普通硅酸盐水泥凝结时间、标准稠度用水量以及水泥胶砂流动性和强度的影响。结果表明,水泥浆体的初凝、终凝时间在矿渣粉掺量为5%(质量分数,下同)时有所缩短,而随着超细矿渣粉掺量的增加,初凝时间都有所延长,在掺量为20%时初凝时间最长。然而终凝时间的变化不大,只有掺量为30%时稍有延长;水泥的标准稠度用水量先减少后增加,在掺量为20%时最小;随着超细矿渣粉掺量的增大,水泥胶砂的各龄期抗折强度、3d抗压强度不断提高,7d、28d抗压强度在掺量为20%时达到最大值,之后有所降低。掺入超细矿渣粉后,能通过填充以及与水泥水化产物氢氧化钙发生反应,使水泥中氢氧化钙含量明显降低,水泥微观结构更加密实。     

Calcium sulphate anhydrite based composite binders; effect of Portland cement and four pozzolans on the hydration and strength

The strength, hydration products, microstructure and heat of early hydration were investigated on alternative hydraulic green cements based on calcium sulphate anhydrite partially blended with Portland cement and pozzolans. Four pozzolans of different physical and chemical nature, namely a geothermal waste, silica fume, metakaolin and pulverized fuel ash were characterized. The composite binders showed hydraulic behavior. The use of Portland cement favoured the strength, which was also higher with the incorporation of siliceous nanometric pozzolans compared to the micrometric silicoaluminate pozzolans. The nanoparticles enhanced the early hydration and changed the gypsum morphology promoting denser matrices of hydration products. The geothermal waste pozzolan was the most effective, while one of the composites with metakaolin showed formation of ettringite and strength losses. The heat of hydration of the composites was considerably lower than that of the neat Portland cement.     

环境湿度对玻璃纤维增强水泥力学性能的影响

通过开展在不同龄期、不同环境湿度下玻璃纤维增强水泥(GRC)试件的抗折强度、抗压强度试验和基体pH值测定,研究了环境湿度对掺加粉煤灰和硅灰等活性矿物掺合料的GRC试件力学性能的影响。结果表明:环境湿度对GRC试件的抗折强度有重要影响,相对湿度越大,随着龄期增加, GRC试件抗折强度降低越严重;在温度60℃、相对湿度95%条件下,经过56 d龄期后,掺有40%粉煤灰和10%硅灰的GRC试件抗折强度比未掺加粉煤灰和硅灰的GRC试件的抗折强度提高48.5%、抗压强度提高23.6%, GRC基体pH值降低6%。在相同的湿度条件下,掺有粉煤灰和硅灰试件的pH值在各个龄期都低于普通硅酸盐水泥试件,说明粉煤灰和硅灰的掺入能降低水泥水化液相的碱度,进而延缓了纤维受侵蚀的速度,显著改善了GRC试件的力学及耐久性能。通过对试验结果进行分析,利用MATLAB软件建立了GRC试件抗折强度和抗压强度与水泥砂浆基体pH值及时间的关系式。      

High replacements of reactive pozzolan in blended cements: Microstructure and mechanical properties

A study comparing silica fume (SF) and dealuminated kaolin (DK) as pozzolanic materials was carried out. 10, 20 or 30-wt.% SF or DK were substituted for Portland cement. The kinetics of hydration were studied at water/solid ratios of 0.30 and 0.50. The hydration reactions were monitored by determining the compressive strengths, the free lime contents and the amounts of combined water. The hydration products were investigated using XRD and SEM/EDX. Both pozzolans increase the total porosities, when used without water reducers or superplasticizers. Both also decreased the compressive strengths at early ages. However, the strengths recovered with time exceed that of the reference Portland cement paste. Strength gain was more rapid in DK mixes than in SF mixes. The optimum content of each pozzolan varied with the water/solid ratios of the blends. Unreacted silica fume, in the highly-substituted mix (30%), caused a reduction in the mechanical properties by providing weak points for the crack propagation.