Effect of nonpozzolanic and pozzolanic mineral admixtures on the hydration behavior of ordinary Portland cement

The effects of nonpozzolanic (marble dust) and pozzolanic (rice husk ash) mineral admixtures on the hydration behavior and mechanical properties of ordinary Portland cement (OPC) have been investigated. The blending of both marble dust (20-60%) and rice husk ash (10-30%) in OPC accelerate the setting as compared to control (OPC). Marble dust addition decreases the strength of OPC and the maximum strength of 54.5 MPa has been achieved on 28 days of curing with 20% of marble dust (CM20). Addition of rice husk ash increases the strength and maximum strength of 65.9 MPa has been observed with 20% of RHA (CR20) blended cement. The formation of various crystalline phases and their effects on hydration behavior of mineral admixtures blended cement were examined by X-ray diffraction (XRD). The changes in microstructure of the hydrated samples were also studied using scanning electron microscope (SEM).     

Effect of rice husk ash on the strength and durability characteristics of concrete

This work investigates the effects of adding residual rice husk ash (RHA) from South Vietnam, generated when burning rice husk pellets in the boiler, to cement. To improve pozzolanic reactivity, RHA was ground for 1 h. The non-ground RHA and ground RHA were used to test strength activity index according to ASTM C311. The properties of the concrete were investigated, including compressive strength, concrete electrical resistivity, and ultrasonic pulse velocity. Results show that the non-ground RHA can be applied as a pozzolanic material. Decreasing the non-ground RHA average particle size provides a positive effect on the compressive strength of mortar. Compressive strength of cylindrical concrete in the 47–66 MPa range was obtained in this study. The results also indicate that up to 20% of ground RHA could be advantageously blended with cement without adversely affecting the strength and durability properties of concrete.     

Properties of cement—rice husk mixture

The properties of lightweight mortar using rice husk can benefit from pozzolanic reaction and from organic fibre reinforcement. The effect of curing and storage on 40×40×160 mm³ OPC rice husk mortar specimens is described. Two conditions are studied; one-year storage at 50% RH and at 95% RH. The final specimen properties were characterised by density, strength, SEM, EDS and XRD. It is concluded that at high humidity storage, pozzolanic reaction is well developed but husk fibres deteriorate. The mortar stored at 50% RH has a lower compressive strength and higher flexural strength, indicating inferior pozzolanic reaction and active fibre reinforcement.     

Corrosion performance of rice husk ash blended concrete

Rice husk ash is one of the promising pozzolanic materials that can be blended with Portland cement for the production of durable concrete and at the same time it is a value added product. Addition of rice husk ash to Portland cement not only improves the early strength of concrete, but also forms a calcium silicate hydrate (CSH) gel around the cement particles which is highly dense and less porous. This may increase the strength of concrete against cracking. So far a systematic and detailed investigations on the corrosion performance of rice husk ash blended concrete is very scarce. Therefore, in the present investigation, a realistic approach has been made using different techniques such as compressive strength, bond strength, split tensile strength etc. Corrosion performance was evaluated using, open circuit potential measurements, rapid chloride ion permeation test and impressed voltage test and the results were discussed.     

Strength and water permeability of concrete containing palm oil fuel ash and rice husk–bark ash

In this paper, palm oil fuel ash and rice husk–bark ash, which are by-products from electricity generating power plants and disposed as wastes in landfills, were used as a partial cement replacement. They were ground and incorporated into concrete at the levels of 20%, 40% and 55% by weight of binder. Compressive strength and water permeability of concretes containing ground palm oil fuel ash (GPOA) and ground rice husk–bark ash (GRBA) were investigated. From the tests, the replacement of Portland cement by both materials resulted in the higher water demand in concrete mixtures as compared to ordinary Portland cement (OPC) concrete with compatible workability. The compressive strengths of concretes containing 20% of GPOA and GRBA were as high as that of OPC concrete and were reduced as the increase in the replacement ratios. Although the compressive strengths of concrete with the replacement of GPOA or GRBA up to 40% were lower than OPC concrete, their water permeabilities were still lower than that of OPC concrete. These results indicate that both of GPOA and GRBA can be applied as new pozzolanic materials to concrete with an acceptable strength as well as permeability.     

Engineering characteristics of the compressed-stabilized earth brick

Utilization of lime and rice husk ash for soil stabilization produced considerable strength gain and other geotechnical properties of the stabilized soils. Its application could be also superior for construction materials as compressed-stabilized earth (CSE) or unfired-brick. This paper presents the investigation result of the application of lime and rice husk for unfired brick or compressed stabilized earth. The compressive and three-point flexural strength tests including compressive strength after water submersion were carried out in this present study. The investigation results show that compressive and flexural strength of clay brick are improved by adding of lime and RHA. The best quantity of lime and RHA in this study, is obtained by ratio 1:1 of lime and RHA. The addition of sand in stabilized clay resulted in more improvement in the water retention ability.     

掺稻壳灰活性粉末混凝土配合比试验

通过试验研究了掺稻壳灰的活性粉末混凝土（RPC）的配合比,根据最大密实度理论对掺稻壳灰的RPC进行了基本配合比设计;试验比较了石英砂和天然砂2种细集料对RPC性能的影响;对不同水胶比的RPC进行试验,推荐了适宜水胶比;以稻壳灰替代硅灰,试验研究不同稻壳灰替代率对RPC的流动性、强度及耐久性的影响。结果表明:采用天然砂替代石英砂作为细骨料对RPC抗折强度、抗压强度及流动度影响不大;掺稻壳灰的RPC的适宜水胶比为0.20~0.22;随着稻壳灰替代硅灰掺量的增加,其收缩率降低且随龄期增长变化减缓,同时其抗氯离子渗透性能有所下降;建议根据不同使用性能要求选择稻壳灰部分或完全替代硅灰的RPC。     

Pozzolanic activity of Hwangtoh clay

Hwangtoh is a clay that has long been used as a traditional Korean building material. In these days, Hwangtoh is often used for plastering and flooring in newly constructed buildings to minimize sick building syndrome. In such applications, it is useful to determine whether the clay has pozzolanic properties. In this research, the pozzolanic activity of Hwangtoh clay was indicated by a reduction in calcium hydroxide and an increase in compressive strength in mortars, in which 20% of the Portland cement was replaced by the clay. The thermally activated Hwangtoh clay showed clear pozzolanic activity at 14 and 28 days, and the as-received clay showed some evidence of pozzolanic activity as well. The compressive strength provided by the activated clay was less than that provided by a synthetic mixture of metakaolin and quartzite, but still greater than that provided by the as-received Hwangtoh. The strength development may be improved further by removing the quartzite from the Hwangtoh clay.     

掺稻壳灰/硅灰混凝土的性能研究

研究了稻壳灰、硅灰、稻壳灰+粉煤灰、硅灰+粉煤灰对混凝土抗压强度、抗折强度、抗硫酸侵蚀能力和抗碳化能力的影响.结果表明:掺加5％～10％稻壳灰或硅灰有助于提升混凝土的抗压强度和抗折强度,且稻壳灰、硅灰掺量越高抗压强度越高,掺硅灰混凝土相对于掺稻壳灰混凝土的抗压和抗折强度更高,掺稻壳灰+粉煤灰、硅灰+粉煤灰试件的抗压和抗...     

Stabilization of residual soil with rice husk ash and cement

Stabilization of residual soils is studied by chemically using cement and rice husk ash. Investigation includes the evaluation of such properties of the soil as compaction, strength, and X-ray diffraction. Test results show that both cement and rice husk ash reduce the plasticity of soils. In term of compactability, addition of rice husk ash and cement decreases the maximum dry density and increases the optimum moisture content. From the viewpoint of plasticity, compaction and strength characteristics, and economy, addition of 6–8% cement and 10–15% rice husk ash is recommended as an optimum amount.     

Assessment of the effects of rice husk ash particle size on strength,water permeability and workability of binary blended concrete

This study develops the compressive strength, water permeability and workability of concrete by partial replacement of cement with agro-waste rice husk ash. Two types of rice husk ash with average particle size of 5 micron (ultra fine particles) and 95 micron and with four different contents of 5%, 10%, 15% and 20% by weight were used. Replacement of cement up to maximum of 15% and 20% respectively by 95 and 5 μm rice husk ash, produces concrete with improved strength. However, the ultimate strength of concrete was gained at 10% of cement replacement by ultra fine rice husk ash particles. Also the percentage, velocity and coefficient of water absorption significantly decreased with 10% cement replacement by ultra fine rice husk ash. Moreover, the workability of fresh concrete was remarkably improved by increasing the content of rice husk ash especially in the case of coarser size. It is concluded that partial replacement of cement with rice husk ash improves the compressive strength and workability of concrete and decreases its water permeability. In addition, decreasing rice husk ash average particle size provides a positive effect on the compressive strength and water permeability of hardened concrete but indicates adverse effect on the workability of fresh concrete.     

普通烧制稻壳灰对水泥胶砂强度的影响

通过等量替代法,研究了普通烧制稻壳灰等量替代水泥后对水泥胶砂强度的影响.结果表明,普通烧制稻壳灰替代率为2％时,试件28 d抗折强度和抗压强度均高于空白胶砂试件,表明掺入少量的稻壳灰有一定的增强作用;稻壳灰替代率为4％时,对胶砂试件的强度影响不明显;稻壳灰替代率＞8％时,胶砂强度降低幅度较大.将普通烧制稻壳灰以低替代率应用于水泥混凝土中是可行的.     

Genetic programming approach for prediction of compressive strength of concretes containing rice husk ash

Soft computing techniques have recently been widely used to model some of human activities in many areas of civil engineering applications. In this paper, two models in gene expression programming (GEP) approach for predicting compressive strength of concretes containing rice husk ash have been developed at the age of 1, 3, 7, 14, 28, 56 and 90 days. For purpose of building the models, experimental results for 188 specimens produced with 41 different mixture proportions are obtained from the literature. According to these experimental results, the models are arranged by using seven different input variables in GEP approach. In according to these input variables, the compressive strength values from mechanical properties of concretes containing rice husk ash are predicted in GEP approach models. The results of training, testing and validation sets of the models are compared with experimental results. All of the results showed that GEP is a strong technique for the prediction of compressive strength values of concretes containing rice husk ash.     

Unconfined compressive strength prediction of soils stabilized using artificial neural networks and support vector machines

This study aims to improve the unconfined compressive strength of soils using additives as well as by predicting the strength behavior of stabilized soils using two artificial-intelligence-based models. The soils used in this study are stabilized using various combinations of cement, lime, and rice husk ash. To predict the results of unconfined compressive strength tests conducted on soils, a comprehensive laboratory dataset comprising 137 soil specimens treated with different combinations of cement, lime, and rice husk ash is used. Two artificial-intelligence-based models including artificial neural networks and support vector machines are used comparatively to predict the strength characteristics of soils treated with cement, lime, and rice husk ash under different conditions. The suggested models predicted the unconfined compressive strength of soils accurately and can be introduced as reliable predictive models in geotechnical engineering. This study demonstrates the better performance of support vector machines in predicting the strength of the investigated soils compared with artificial neural networks. The type of kernel function used in support vector machine models contributed positively to the performance of the proposed models. Moreover, based on sensitivity analysis results, it is discovered that cement and lime contents impose more prominent effects on the unconfined compressive strength values of the investigated soils compared with the other parameters.     

Origin of the pozzolanic effect of rice husks

Rice husk ash has been used in many countries as a low cost concrete admixture because of its role as a filler and a pozzolan. A study is made of an ash produced in Senegal to establish the existence and origin of silica. Two calcinated rice husk ashes were studied. X-Ray diffraction analysis revealed the presence of quartz whose origin may be attributed to contamination and/or re-crystallisation of silica in the calcination. Amorphous silica was detected by scanning electron microscopy and microanalysis, its presence is concentrated on the interior and exterior surfaces of the uncalcinated husk which may promote a pozzolanic action on the surface of the husk and therefore enable its use in lightweight concrete.     

Influence of the use of rice husk ash on the electrical resistivity of concrete: A technical and economic feasibility study

This study investigated the behavior of apparent electrical resistivity of concrete mixes with the addition of rice husk ash using Wenner’s four electrode method. Tests included compressive strength, porosity and electrical conductivity of the pore solution. The contents of rice husk ash tested were 10%, 20% and 30% and results were compared with a reference mix with 100% Portland cement and two other binary mixes with 35% fly ash and 50% blast furnace slag. Higher contents of rice husk ash resulted in higher electrical resistivity, which exceeded those of all other samples. However, for compressive strength levels between 40 MPa and 70 MPa, the mix with 50% blast furnace slag showed the best combination of cost and performance.     

Pozzolanic behaviour of bagasse ash

The CBRI investigations indicate that bagasse ash has to be considered as a pozzolanic material like fly ash or any other conventional pozzolana. High surface area is required to expose the grains which are coated with iron oxide and carbonaceous impurities. The authors consider that the material may be used for preparing lime ash mixture to be used locally as a mortar, especially in rural areas where availability is high.     

Effect of pozzolanic admixtures on mechanical,thermal and hygric properties of lime plasters

Compressive and bending strength, thermal conductivity, specific heat capacity, water sorptivity, moisture diffusivity, water vapor diffusion coefficient, sorption isotherms, and linear thermal and hygric expansion coefficients of three lime plasters with pozzolanic admixtures are determined in the paper. Comparative measurements with common lime plaster are done as well. On the basis of the experiments performed, it can be concluded that all the three analyzed lime-pozzolana plasters are suitable for an application in reconstruction of historical buildings. While their mechanical properties are significantly better compared to the reference lime plaster, their thermal and hygric properties are mostly similar or slightly improved. The only parameter that is found to be worse than for the common lime plaster is the linear hygric expansion coefficient but its worsening can be matched by the improved mechanical properties.     

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.     

黑液粉煤灰烧结砖的研制

本文以粉煤灰为主要原料、少量粘土为粘结剂、改性黑液为成型剂进行了烧结砖研制。讨论了粉煤灰与黑液用量对烧结砖性能的影响 ,并通过正交试验求出最佳配比与工艺参数。试验结果表明 ,这种烧结砖可达到GB50 10— 85标准中MU15级的要求 ,且比普通粘土烧结砖质量轻、保温性能好。