Sulfate resistance of the cement materials based on the modified silica fume

The object of the study was the influence of chemically modified silica fume (MSF) on the sulfate resistance of cement-based materials. MSF is a liquid product prepared from a suspension of silica fume and a water solution of a reactant under the defined composition of suspension, defined ambient temperature and time of procedure. MSF is added into mortar or concrete mixtures instead of water in the quantities needed for the desired consistency. The results obtained at the application of MSF shows a significant increase of sulfate resistance of materials based on Portland cement slag blends and slag binder. This positive effect represents a further beneficial potential of MSF that has already been shown as an effective hardening accelerator together with its ability to increase the acidic resistance of materials based on Portland cement slag blends and slag binder.     

Acidic resistance of materials based on the novel use of silica fume in concrete

The objectives of this paper are the results of a study on the acidic resistance of cement-based materials prepared with chemically modified silica fume (MSF). MSF seems to be a highly effective hardening accelerator of materials based on combinations of Portland cement and basic blast furnace slag and on this slag alone. Besides the mechanical properties chemical resistance is a very important engineering property of concretes. This is very interesting even with cement-based materials with a MSF application. It was a reason for the study on the acidic resistance of the cement-based materials when MSF was applied. Based on the observation of changes of chemical composition, pore structure and mechanical properties of the test specimens, a high acidic resistance was found on the cement-based materials when MSF was applied. This allowed a solution to the problem of insufficient acidic resistance of current cement-based materials which represents a crucial world-wide problem.     

Stabilization of marginal aggregates with hydraulic and puzzolanic binders based on waste materials

Natural sand deposits and waste screenings from gravel pits and quarries are abundant in parts of Sweden. Investigations have been made to stabilize such materials with binders based on waste materials. Both laboratory work and test roads have been performed. In the latter case, mainly secondary roads have been strengthened with a plant-mixed bases. Good results have been achieved with a binder made of milled granulated blast furnace slag, activated with lime or especially with both lime and waste gypsum. Sand and screenings from gravel often contain organic material, deleterous with the binders studied. In such cases, the gypsum addition also seems to counteract the negative effect of the organic material. Fly ash has recently been available in Sweden. Tests made with fly ash-lime, as often used for stabilization abroad, have shown too slow binding for a rather cold climate. Addition of waste gypsum, calcium chloride, alkali-salts or use of an alkali-rich cement kiln dust instead of commercial lime can improve the binding properties. Different fly ashes, however, react in different ways. It is often more suitable to use fly ash-cement as a binder, especially with poorly graded aggregates. The fly ash, added in an optimum amount, work as a filler and high immediate stabilities can be achieved at a correct water content. The puzzolanic properties of the fly ash, at the same time, makes it possible to reduce the cement content considerably in comparison with the case when only portland cement is used as a binder. Promising laboratory work has also been done with binders consisting of condensed silica fume or ash from fluidized bed coal combustion, both in combination with lime.     

Mechanical and durability properties of high performance concretes containing supplementary cementitious materials

An experimental investigation was carried out to evaluate the mechanical and durability properties of high performance concretes containing supplementary cementitious materials in both binary and ternary systems. The mechanical properties were assessed from the compressive strength, whilst the durability characteristics were investigated in terms of chloride diffusion, electrical resistivity, air permeability and water absorption. The test variables included the type and the amount of supplementary cementitious materials (silica fume, fly ash and ground granulated blast-furnace slag). Portland cement was replaced with fly ash up to 40%, silica fume up to 15% and GGBS up to a level of 70%.The results confirmed that silica fume performs better than other supplementary cementitious materials for the strength development and bulk resistivity. The ternary mixes containing ground granulated blast-furnace slag/fly ash and silica fume performed the best amongst all the mixes to resist the chloride diffusion. The mix containing fly ash showed favourable permeation results. All the ternary combinations can be considered to have resulted in high performance concretes with excellent durability properties.     

内掺锂渣和硅粉的100MPa高强度大流动性混凝土研究

研究了内掺锂渣和硅粉对混凝土强度和流动性的影响 ;根据试验数据总结出内掺锂渣和硅粉混凝土的 2 8d抗压强度规律 ,研究了混凝土后期强度的增长规律 ;采用 4 2 5普通硅酸盐水泥、中砂、5～ 2 5mm碎石 ,内掺 10 %～ 15 %锂渣和 5 %硅粉 ,水胶比 0 2 5 5～ 0 2 6 8,或内掺 0～ 15 %锂渣和 10 %硅粉 ,水胶比 0 2 6 0～0 30 5 ,掺加适量的NF - 2 - 6缓凝高效减水剂 ,可配制出 10 0MPa高强度大流动性混凝土。     

硅灰和粉煤灰在200 MPa活性粉末混凝土中的应用机理

活性粉末混凝土(RPC)由于具有超高强度、韧性及耐久性而得到快速推广应用。采用0.14的极低水胶比制备200 MPa的RPC,并测试硅灰和粉煤灰对RPC强度和微结构的影响。研究结果表明:RPC的强度随着硅灰掺量的增加呈现先增大后减小的趋势,随着粉煤灰掺量的增加而减小,适量的硅灰掺量和较小的粉煤灰掺量有助于RPC获得较高的强度。硅灰和粉煤灰均具有较高的填充效应和火山灰活性,其活性二氧化硅可与氢氧化钙水化生成水化硅酸钙,尤其是颗粒极细的硅灰,可大幅改善浆体微结构,提高RPC的强度。     

Evaluation of coatings,mortars and mix design for protection of concrete against sulphur oxidising bacteria

Deterioration of concrete in cooling tower basins by microbiologically influenced corrosion (MIC) is a concern in geothermal power plants. The effect of supplementary cementitious materials, epoxy coatings, latex-modified mortars and calcium aluminate cement mortar for protecting concrete from MIC was investigated. Laboratory exposure tests to a particular type of sulphur and iron oxidising bacteria, Thiobacillus ferrooxidans, were performed to rank candidate materials and these were followed by field exposure tests of the best materials in a cooling tower basin. It was determined that partial replacement of cement with 40% blast furnace slag or 5% to 10% silica fume improved resistance to MIC. A replacement level of 60% slag resulted in similar performance to concrete made with ordinary Portland or sulphate resistant cement. Epoxy- and styrene butadiene latex-modified mortars offered protection to concrete but still underwent a degree of attack. Epoxy coatings were found to be effective in protecting concrete. Calcium aluminate cement mortar showed excellent durability in laboratory and field tests.     

Properties of blended sulfoaluminate belite cement

The subject of the study was the possibility of the blending of sulfoaluminate belite (SAB) cement by means of various pozzolanas. The results obtained show that it was possible effectively to modify the properties of SAB cement by means of granulated blast furnace slag, fly ash, and silica fume, and the properties of materials based on these blends. Interesting properties from practical viewpoints of these materials was their compressive strength. As it is very well known, this is by the blending used to decrease. From a viewpoint of the acceptable compressive strength decrease, for SAB cement blends well-found portions of pozzolana with the values of approximately 5–15% seem to be optimal. This range was significantly lower than well-found portions of pozzolanas with values of approximately 20–40% for Ordinary Portland Cement (OPC) blends. The main cause was the fact that unique sources of calcium hydroxide needed for pozzolanic reaction in SAB was only β–C₂S compared to OPC having two sources of calcium hydroxide — the hydration of C₃S and β–C₂S. Therefore, the amount of calcium hydroxide for the pozzolanic reaction in the SAB cement blends was significantly lower. That was why the lower portions of pozzolanas in SAB cement blends were suitable.     

Use of binary and ternary blends in high strength concrete

Combinations of cement additions may provide more benefits for concrete than a single one. In this study, 80 high strength concretes containing several types and amounts of additions were produced. In the first stage, silica fume contents in binary blends that give the highest strengths were determined for different binder contents. In the second stage, a third binder (Class F or Class C fly ash or ground granulated blast furnace slag) was introduced to the concretes already containing Portland cement and silica fume in the amounts found in the first stage. Results indicated that ternary blends almost always made it possible to obtain higher strengths than Portland cement + silica fume binary mixtures provided that the replacement level by the additions was chosen properly. Moreover, the performance of slag in the ternary blends was better than Class F fly ash but worse than Class C fly ash.     

Effect of silica fume on cement hydration and temperature rise of concrete in tropical environment

Investigated herein is the effect of temperature on heat development in cement pastes and concretes with and without silica fume cured at relatively high temperatures often encountered in tropical environment. With an initial temperature of 30°C, adiabatic temperature rise of the concrete with 8% silica fume as cement replacement was similar to that of the control Portland cement concrete up to about 18 h. After 24 h, however, the temperature of the silica fume concrete was lower than that of the control concrete. Since the concrete with 8% silica fume had a higher 28-day compressive strength (72.5 MPa) than the control concrete without silica fume (59.2 MPa), the concrete with silica fume is likely to have a lower temperature rise as compared with the control concrete of equivalent 28-day strength by reducing cementitious materials content with the same water content. The extent of heat evolution in the silica fume pastes was generally greater at lower temperatures of 20-50°C, but less at 65°C than in the control paste. At the relatively high curing temperatures, the degree of cement hydration in the paste with silica fume was lower than that in the control cement paste at early ages. However, the pozzolanic reaction started even before 24 h after water was added.     

Effect of silica fume on cement hydration and temperature rise of concrete in tropical environment

Investigated herein is the effect of temperature on heat development in cement pastes and concretes with and without silica fume cured at relatively high temperatures often encountered in tropical environment. With an initial temperature of 30°C, adiabatic temperature rise of the concrete with 8% silica fume as cement replacement was similar to that of the control Portland cement concrete up to about 18 h. After 24 h, however, the temperature of the silica fume concrete was lower than that of the control concrete. Since the concrete with 8% silica fume had a higher 28-day compressive strength (72.5 MPa) than the control concrete without silica fume (59.2 MPa), the concrete with silica fume is likely to have a lower temperature rise as compared with the control concrete of equivalent 28-day strength by reducing cementitious materials content with the same water content. The extent of heat evolution in the silica fume pastes was generally greater at lower temperatures of 20–50°C, but less at 65°C than in the control paste. At the relatively high curing temperatures, the degree of cement hydration in the paste with silica fume was lower than that in the control cement paste at early ages. However, the pozzolanic reaction started even before 24 h after water was added.     

High performance concrete with Czech metakaolin: Experimental analysis of strength,toughness and durability characteristics

Although the capability of metakaolin as pozzolanic material to improve mechanical and durability properties of concrete if used as partial replacement of Portland cement is well noted in concrete science, its utilization in building industry was limited to date, mainly due to its high price dictated by the low production amounts. However, with the current shortage of silica fume and high-quality slag in some countries the attitude of concrete producers to metakaolin may change in the near future. This change of mind can be facilitated by providing a more comprehensive view of the properties of composite materials with metakaolin, thus contributing to wider realization of the benefits of metakaolin in concrete. In this paper, an extensive set of parameters of high performance concrete (HPC) with metakaolin including basic physical characteristics, mechanical and fracture-mechanical properties, durability characteristics, hydric and thermal properties and chloride binding characteristics is measured. The experimental results show that the replacement of Portland cement by 10% of metakaolin as an optimal amount leads in most cases either to improvements or at least does not significantly impair substantial properties of the analyzed HPC. Basic physical properties and heat transport and storage properties are very similar to common HPC, mechanical and fracture-mechanical properties after 28 days are slightly worse but later improved, water- and water vapor transport parameters are substantially reduced, frost resistance is better, resistance against de-icing salts is slightly worse but still meets very well the required criteria. The chemical resistance of concrete with 10% of metakaolin instead of Portland cement in distilled water and HCl is found better than for Portland cement concrete, in MgCl₂ it is slightly worse, and in NH₄Cl, Na₂SO₄ and CO₂ almost the same, carbonation is reduced, and chloride binding capacity is increased.     

Interaction between C3A,silica fume and naphthalene sulphonate superplasticiser in high performance concrete

In high performance concrete, fillers and superplasticisers are typically added to the binder system. It is clear that cement, filler and admixture interact, and influence concrete properties. By means of an experimental programme on concrete with different types of Portland cement, with and without partial cement replacement by silica fume, and considering a naphthalene sulphonate superplasticiser, the interaction between C₃A, silica fume and naphthalene sulphonate superplasticiser has been investigated.A higher C₃A content of the Portland cement leads to a higher required dosage of superplasticiser. Partial cement replacement by silica fume leads to an acceleration of the second hydration peak (hydration of C₃S). Early age strength development of the concrete is higher in case of a higher C₃A content.     

C100高强度大流动性混凝土的试验研究

分析了高强度大流动性混凝土的技术特点 ,研究了内掺硅粉量 ( % )及水泥品种对混凝土强度和流动性的影响 ;根据试验数据总结出混凝土 2 8d的强度规律 ;采用 42 5硅酸盐水泥或普通硅酸盐水泥、内掺硅粉量 10 %～ 15 %、中砂或粗砂、5～ 2 5mm碎石、掺加适量的NF -2 -6缓凝高效减水剂 ,水胶比不大于 0 2 9,能配制出C10 0高强度大流动性混凝土。     

The influence of gypsum ratio on the mechanical performance of slag cement accelerated by calcium sulfoaluminate cement

This paper investigates the use of calcium sulfoaluminate cement to improve the strength of high-grade slag cement composed of granulated blast-furnace slag and anhydrite. Two quaternary binders, composed of granulated blast-furnace slag, Portland cement, calcium sulfoaluminate clinker and calcium sulphate are compared with the reference. The only parameter studied is the gypsum ratio in the calcium sulfoaluminate cement. The results of compressive strength testing on standard mortar (in accordance with the European standard NF EN 196-1) indicate that the early and medium-term mechanical performances increase as the amount of gypsum increases. To explain this, pore size distribution in the mortar was studied and XRD, DTA–TGA and SEM techniques were applied to pure paste. The investigation showed that the hydration reactions of the individual constituents are dependent on the gypsum ratio and that its variation can lead to the formation of different hydrates.     

Influence of dry and wet curing conditions on compressive strength of silica fume concrete

This paper reports a part of an ongoing laboratory investigation in which the compressive strength of silica fume concrete is studied under dry and wet curing conditions. In the study, a total of 48 concretes, including control Portland cement concrete and silica fume concrete, were produced with four different water–cement ratios (0.3, 0.4, 0.5, 0.6), three different cement dosages (350, 400, 450 kg/m³) and three partial silica fume replacement ratios (10%, 15%, 20%). A hyperplastisizer was used in concrete at various quantities to provide and keep a constant workability. Three cubic samples produced from fresh concrete were demoulded after a day; then, they were cured at 20±2 °C with 65% relative humidity (RH), and three other cubic samples were cured at 20±2 °C with 100% RH until the samples were used for compressive strength measurement at 28 days. The comparison was made on the basis of compressive strength between silica fume concrete and control Portland cement concrete. Silica fume concretes were also compared among themselves. The comparisons showed that compressive strength of silica fume concrete cured at 65% RH was influenced more than that of Portland cement concrete. It was found that the compressive strength of silica fume concrete cured at 65% RH was, at average, 13% lower than that of silica fume concrete cured at 100% RH. The increase in the water–cementitious material ratios makes the concrete more sensitive to dry curing conditions. The influence of dry curing conditions on silica fume concrete was marked as the replacement ratio of silica fume increased.     

矿物掺合料对硫铝酸盐水泥-普通硅酸盐水泥复合体系性能的影响

研究了矿粉、硅灰和粉煤灰3种矿物掺合料对硫铝酸盐水泥-普通硅酸盐水泥复合体系的标准稠度用水量、凝结时间、水化放热、胶砂抗折及抗压强度、砂浆干缩率、抗硫酸盐侵蚀性能和水化产物的影响。结果表明:随矿物掺合料掺量的增加,复合体系的标准稠度用水量增大,凝结时间延长;掺加矿物掺合料后水化放热峰出现时间延后,总水化放热量减少,其中掺加矿粉和硅灰的试件初期水化速率减慢程度较掺加粉煤灰试件更明显;3种矿物掺合料对复合体系强度的影响差别较大,掺加3%硅灰的试件3 d抗压强度增长较快;硅灰的掺加会使砂浆干缩率增大,矿粉、粉煤灰的掺加可以减小砂浆试件的干缩;矿物掺合料的掺加会提高胶砂试件抗硫酸盐侵蚀性能,掺粉煤灰的试件抗硫酸盐侵蚀性能最好。     

硅灰对硫铝酸盐水泥水化行为的影响机理

通过抗压强度、凝结时间、电阻率测定以及X射线衍射(XRD)、扫描电镜(SEM)和孔溶液分析,研究了掺硅灰硫铝酸盐水泥浆体的水化行为.结果表明:5%掺量(质量分数,下同)的硅灰可以很好地改善水泥浆体的抗压强度,10%硅灰掺量的试样抗压强度只在1,28d时稍高于空白试样;掺入硅灰明显缩短了硫铝酸盐水泥的凝结时间;硫铝酸盐水泥的主要晶体水化产物是钙矾石,28d时的钙矾石量稍高于3d时,掺硅灰试样的钙矾石量要高于空白试样;掺硅灰试样的电阻率变化曲线高于空白试样,表明硅灰的掺入能够加快水泥的水化速率;硬化水泥浆体的孔溶液碱度随着硅灰掺量的增加而降低,掺硅灰试样的Ca2+浓度高于空白试样,表明硅灰促进了熟料的溶解,5%硅灰掺量试样的Al 3+浓度最低,表明其促进水化的效果更明显.     

内掺钢渣、硅粉的C80高性能混凝土研究

研究了钢渣、硅粉掺量对混凝土强度与流动性的影响以及钢渣、硅粉混凝土强度规律。采用4 2 5普通硅酸盐水泥、中砂、5～ 2 5mm碎石、掺加适量NF 2 6缓凝高效减水剂 ,水胶比 0 2 6 ,钢渣、硅粉掺量均为 10 %或水胶比 0 2 4～ 0 31,钢渣掺量 10 %～ 30 % ,硅粉掺量 15 % ,可配制C80高性能混凝土 ,并给出了混凝土配合比参考公式。     

Hydration heat kinetics of concrete with silica fume

The objective of this study was to evaluate the influence of silica fume on the hydration heat of concrete. Portland cement was replaced by silica fume in amounts from 10 % to 30 % by mass in concrete with w/(c+sf) ratios varying between 0.25 and 0.45. A superplasticizer was used to maintain a fluid consistency. The heat of hydration was monitored continuously by a semi-adiabatic calorimetric method for 10 days at 20 °C. The calorimetric study indicated that the hydration was modified by the presence of silica fume. In the early stages, the silica fume showed a high activity and accelerated the hydration rate as compared to that of the reference concrete. The fine silica fume particled provided nucleation sites for hydrates growth. Then the pozzolanic activity took over and increased both strength and the hydration heat. A substitution of Portland cement by 10% with silica fume produced greater strength and cumulative heat of hydration as compared to that of the reference concrete.