偏高岭土作混凝土掺和料的应用性能研究

高岭土在经700～800℃热处理后得到新型高活性混凝土偏高岭土(Metakaolin)矿物掺和料,所配制的混凝土具有良好的力学性能和耐久性能。本文详细介绍了MK掺和料的火山灰特征及在混凝土中的应用机理,以及国内外偏高岭土的研究现状和应用前景。     

偏高岭土的制备及其在混凝土中的应用

高岭土在经700～800℃热处理得到新型高活性混凝土偏高岭土（Metakaolin）矿物掺和料，所配制的混凝土具有良好的力学性能和耐久性能，是一种可持续发展的绿色建筑材料。本文详细介绍了MK掺和料的火山灰特征及在混凝土中的应用机理，以及国内外偏高岭土的研究现状和应用前景。     

偏高岭土矿物掺和料应用性能研究

高岭土在适当的温度下煅烧 ,得到新型高活性混凝土偏高岭土 (KP)矿物掺和料 ,本文详细介绍了KP掺和料在新拌混凝土中的工作性能和硬化混凝土的增强性能 ,同时与硅灰做了对比。试验结果表明 ,偏高岭土是一种良好的矿物掺和料 ,各种性能与硅灰相近 ,完全可以替代硅灰在高性能混凝土中应用     

石膏改性偏高岭土对混凝土抗渗性的影响

将石膏改性偏高岭土应用于水泥基材料中,研究了改性掺和料对混凝土抗压强度、电通量和抗渗性的影响,并对其影响机理进行了探讨。结果表明:石膏改性偏高岭土能够有效改善混凝土的抗压强度,提高其抗渗性;石膏可以优化偏高岭土的二次水化产物,增加混凝土的密实度。     

偏高岭土对混凝土抗氯离子渗透性能的影响及机理研究

以偏高岭土作为矿物掺和料,研究了偏高岭土的掺量对混凝土抗氯离子渗透性能的影响,并对其作用机理进行了探讨。结果表明:随着偏高岭土掺量的增加,混凝土的抗压强度和抗氯离子渗透能力增强;偏高岭土中的C_3A与氯离子形成Friedel盐,通过固化作用有效地阻止了氯离子的渗透。     

偏高岭土混凝土抗冻融性能试验研究

在固定水胶比下,对单掺偏高岭土、偏高岭土与矿粉双掺及偏高岭土、矿粉与粉煤灰复掺的高强混凝土进行力学和快速冻融循环试验,研究掺量对混凝土性能的影响。结果表明:在单掺偏高岭土时,随着掺量增加,混凝土的抗冻性及抗压强度逐渐增强;在偏高岭土与矿粉双掺且取代水泥量为定值时,偏高岭土与矿粉存在最优配合比使混凝土抗冻性及抗压强度最好;在偏高岭土、矿粉与粉煤灰复掺且取代水泥量为定值时,三者之间存在最优配合比使混凝土的抗冻性及抗压强度最好;当复合掺和料取代水泥的量相同时,三元复掺的混凝土抗冻性和抗压强度最好。     

偏高岭土在高强混凝土中的应用

通过各种试验全面介绍了偏高岭土在高强混凝土中的应用,其中对偏高岭土煅烧温度进行了剖析,得出750℃是最佳的煅烧温度;偏高岭土作为活性掺合料的掺量宜为10%左右,超过量使得混凝土用水量增加影响混凝土的工作性和抗压强度,提出了用偏高岭土替代硅灰的可行性。     

预拌混凝土中固废复合掺和料的应用

在现代混凝土技术发展中加入矿物掺和料具有重要现实意义,将工业固废掺和料取代传统混凝土施工中的部分水泥,有助于增强混凝土强度和耐久性,还能使得绿色高性能混凝土在建筑行业实现大面积的推广和应用。从固废复合掺和料概述着手,分析了预拌混凝土中固废复合掺和料的具体应用及其对混凝土性能造成的影响,旨在利用新型复合掺和料提高预拌混凝土使用的强度及性能。     

矿物掺和料对轻集料混凝土性能的影响

通过近年来矿物掺和料在轻集料混凝土中的研究和应用,总结了矿物掺和料对轻集料混凝土的工作性、力学性能和耐久性方面的影响,通过分析作用机理得知使用矿物掺和料能大大提高轻集料混凝土的塌落度、强度、抗渗性和抗冻性。同时,矿物掺和料在轻集料混凝土中的应用还有效解决粉煤灰和矿渣的综合利用问题,实现资源利用的可持续发展。     

硅粉和偏高岭土对混凝土抗压强度影响的试验研究

本文对不同掺量的硅粉和偏高岭土进行单掺和复掺,测试混凝土立方体抗压强度,并对试验结果进行分析。试验结果表明:硅粉和偏高岭土均能增加混凝土的抗压强度,当单掺掺量为10%时抗压强度达到最大值;同等掺量下,相比于单掺硅粉和偏高岭土,将其复掺可以更大幅度地提高混凝土抗压强度;将硅粉和偏高岭土复掺的火山灰效应低于同等掺量下其各自单掺的火山灰效应,也低于总掺量相等时其各自单掺的火山灰效应之和。     

Effect of Portuguese metakaolin on hydraulic lime concrete using different curing conditions

Hydraulic lime concrete with the addition of metakaolin in various percentages and cured under different conditions was studied in order to evaluate the effect of the pozzolanic additions over time (7, 28, 90 and 360 days). This study was performed using NHL 5, a metakaolin of Portuguese origin, siliceous sand and calcareous coarse aggregate, with increasing percentages of substitution of hydraulic lime by metakaolin in weight. In order to evaluate the pozzolanic effect, compressive strength test were performed and analysed by relative strength–time plots and by the application of different indexes such as the index of specific strength and the pozzolanic index. Thermogravimetric analysis was performed at the age of 28 days in order to evaluate the phases present in the concrete specimens. As main conclusions metakaolin is an adequate material for application in concrete with hydraulic lime binder as a pozzolanic addition providing an increase in mechanical strength for the studied substitutions of 20% and 30%. Testing should be performed at 28 days when portlandite consumption is complete.     

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.     

Study of the reactivity of cement/metakaolin binders at early age for specific use in steam cured precast concrete

The paper presents the results of a hydration study performed in order to explain the significant increase in compressive strength at one day of age observed on steam cured mortars when 25% by mass of cement was replaced with a metakaolin. Two CEM I 52.5R cements, differing in reactivity, and a metakaolin (MK) were used. By means of XRD and thermal analysis carried out on cement pastes, blended or not with MK, the main results showed that the improvement in strength at one day of age could be explained by the occurrence of a pozzolanic reaction due to MK, thermo-activated by the high curing temperature (55 °C). The pozzolanic reaction was observed through the consumption of calcium hydroxide and an increase in the amount of C–S–H and C–S–A–H hydrated phases. This change in the hydration product nature and amount was more pronounced when MK was combined with the less reactive cement, in agreement with the mechanical results on mortars. These results are of great importance for the concrete industry where the current trend is to decrease the clinker content in cements (1 ton of clinker = 1 ton of CO₂ released). In particular, the interesting mechanical performance at early ages can be helpful for precast concrete manufacturing.     

Metakaolin sand–blended-cement pastes: Rheology,hydration process and mechanical properties

In the present work, the use of three Slovak poor metakaolin sands with different metakaolin content (36.0% (MK-1), 31.5 (MK-2) and 40.0% (MK-3)) and specific surface has been deeply studied as mineral addition for Portland cement. The percentage of metakaolin sands in the blended cements was 10%, 20% and 40%.The pozzolanic tests confirm that the three metakaolin sands show a high pozzolanic activity, comparable to a commercial metakaolin and silica fume. With respect to the rheological behaviour, metakaolin sand–blended-cement pastes fit to Herchel–Bulkley model and their yield stress increases as the metakaolin content increases. MK-3 sand with the highest pozzolanic activity and highest specific surface induces the highest increase of the yield stress.From the calorimetric results it is concluded that the addition of MK-1 and MK-2 sands to Portland cement induces a delay up to 2 h of the precipitation of the main hydration products in the blended-cement pastes and decreases the maximum heat evolution rate. On the contrary, the incorporation of 40% of MK-3 sand shortens 6 h its apparition and increases significantly the maximum heat evolution rate. Additionally, the presence of the metakaolin sands reduces the heat released during the hydration process with respect to non-blended-cement pastes.The incorporation of metakaolin sand induces a decrease of the mechanical strength, being the decrease higher as the metakaolin sand content increases although they also produce a refinement in the pore structure and a decrease of the permeability.     

Properties of blended cements with thermally activated kaolin

Kaolin, one of the materials of major importance for the ceramic and paper industry, is also used in the construction industry as a raw material for the production of white cement clinker and, in the form of metakaolin, as an artificial pozzolanic additive for concrete. Metakaolin is a vital component of high-performance and architectural concrete; however, its application in regular concrete is very limited due to relatively high production costs. This report evaluates the performance of a low-cost metakaolin-based additive called thermally activated kaolin (TAK), in cement. Due to its pozzolanic properties and the densification of cement matrix, the application of TAK provides a 15% improvement of the compressive strength. It was shown that TAK of optimal quality can be manufactured by the thermal treatment of raw kaolin with 74% of kaolinite at 750 °C without the intermediate beneficiation stage. The application of a developed approach can significantly reduce production expenditures and make the application of such an additive feasible even in regular-grade cement and concrete.     

Increasing mortar strength with the use of activated kaolin by-products from paper industry

Making use of industrial by-product or waste clay to partially replace cement in concrete has greatly contributed to sustainable development of environment. This study investigated the optimal activation condition for producing high reactivity metakaolin (MK) by using kaolin by-products (KB) from paper industry. Initially, the material properties of KB were analyzed in this study and the results indicated its great potential to be treated by calcination to be a very effective pozzolan. Afterwards, MK samples produced from different activation treatments of KB, including different calcining temperature, calcining duration, initial temperature rise rime and grinding particle size, were applied in mortar to determine their pozzolanic effect. Results indicated that the optimal activation condition for KB to high reactivity MK conversion is 2-h calcining duration at 750 °C and with 7 μm grinding particle size. Finally, compressive and flexural strengths of mortar samples produced by replacing cement with 0–25% MK content were tested and the results showed that 15% was the optimal cement replacement level of MK and the mortar so produced exhibited 20% improvement in compressive strength compared to control mortar.     

利用电石渣改性固硫灰制备胶凝材料的研究

基于固硫灰自身的火山灰活性和自硬性,提出用钙质激发剂激发固硫灰活性制备固硫灰基胶凝材料。实验研究表明在激发剂的作用下,掺入偏高岭土后胶凝材料强度提高80%以上。用内掺50%偏高岭土的固硫灰,采用电石渣或熟石灰复合水玻璃作为激发剂制备胶凝材料都在体系的碱含量为30%,水玻璃的模数为2.0,养护温度为60℃时强度达到最大,两种激发剂对强度的影响差异不大,而采用电石渣作为激发剂更节约成本,更具优势。     

Influence of calcined kaolin on mortar properties

The use of calcined clay, in the form of metakaolin (MK), as a pozzolanic material for mortar and concrete has received considerable attention in recent years. The present paper describes the results of a research project initiated to study the calcination of local kaolin at various temperatures (650–950 °C) and durations (2, 3 and 4 h) to produce MK with a high pozzolanic activity. The pozzolanic activity was assessed by 28-days compressive strength and hydration heat methods. The maximum identified activity was obtained at 850 °C for 3 h duration. An increase of both hydration heat and compressive strength was obtained when ordinary Portland cement was replaced by 10% MK. The use of ternary blended cement improves the early age and the long-term compressive strength. The durability was also enhanced as better acidic resistance was observed.     

Study on the pozzolanic properties of a natural Cuban zeolitic rock by conductometric method: Kinetic parameters

Natural zeolite is a type of mineralogical material containing large quantities of reactive SiO₂ and Al₂O₃. These materials have been used in the cement industry as a supplementary cementing material. Like other pozzolanic materials the zeolite contributes to improve the mortar and concrete performances mainly through the pozzolanic reaction with calcium hydroxide (CH). The pozzolanic reactivity of this type of material in comparison with other pozzolans is of great interest.The current paper presents a study about the pozzolanic activity of a natural Cuban zeolitic rock. The pozzolanic activity in a zeolitic material/CH solution is investigated by means of electrical conductivity measurements and latter on the kinetic parameters are quantified by applying a kinetic–diffusive model to process. The kinetic parameters that characterize the process (in particular the reaction rate constant) were determined in the fitting process of the model. The index of pozzolanic activity evaluated according to the obtained values of the reaction rate constant permits to characterize the pozzolanic activity of these materials in a rigorous way.The results show that this Cuban zeolitic rock is a natural material with high pozzolanic activity. Also, these results allow corroborating the direct influence of the fineness of zeolitic material on the pozzolanic and mechanical properties.