粉煤灰和石灰岩石粉对泡沫混凝土抗压强度的影响研究

以昆明市巫家坝城市新中心某市政工程为依托,测试不同水胶比及干密度下泡沫混凝土的无侧限抗压强度(UCS),旨在探究掺合料类型、干密度以及水胶比对其无侧限抗压强度的影响。寻求出各因素对无侧限抗压强度的影响机制,并构建了无侧限抗压强度预测模型,以满足工程实践要求。结果表明:在高水胶比时,粉煤灰对泡沫混凝土UCS有积极作用,但提升程度小,而石灰岩石粉对其则具有显著的衰减作用;泡沫混凝土的UCS随干密度的增加而增长,且粉煤灰对UCS的提高幅度大于石灰岩石粉;当掺合料采用粉煤灰时,水胶比为0.40时的UCS更大;当掺合料是石灰岩石粉时,0.35的水胶比更能提升泡沫混凝土的UCS;灰色关联分析表明干密度与UCS间的关联程度大于水胶比,且构建的预测模型具有较高精度。

石灰岩石粉代替粉煤灰在柬埔寨甘再水电站大坝碾压混凝土中的应用

柬埔寨甘再水电站工程拦河重力坝是百米级全断面碾压混凝土坝,由于当地无粉煤灰、火山灰等掺合料,参照中国石灰石硅酸盐水泥研究成果,进一步试验研究石灰岩粉代替粉煤灰,并逐步实施。探索出一条用石灰岩石粉替代粉煤灰的新路子。经实践证明技术经济效果明显。

磨细石灰岩石粉作常态混凝土混合材研究与应用

用石灰石作混合材生产硅酸盐水泥,国内外已有成功的运用经验,并制定了相应的行业规范。磨细石粉作为常态混凝土混合材的应用与研究,相关的资料还比较少。文章以磨细石粉在柬埔寨甘再电站大工程实际使用为基础,探讨了石灰石作常态混凝土混合材对混凝土施工性能的影响,并研究了磨细石粉掺入混凝土后,对混凝土力学、变形及耐久性的影响。

石灰岩粉作为混凝土掺合料的应用与研究

用磨细石灰岩石粉作为混凝土掺合料,能够降低工程成本,扩大掺合料资源来源。尤其对那些参照美国ASTM标准生产和使用纯硅酸盐TYPEⅠ水泥,而粉煤灰、矿渣、火山灰等掺合料又短缺的国家或地区,使用石粉作为掺合料浇筑大体积混凝土结构物具有更大的实践价值。本文介绍了磨细石粉在柬埔寨甘再水电站碾压(常态)混凝土工程应用的实际情况,探讨了石灰岩作掺合料对碾压混凝土施工性能的影响,并试验研究了磨细石粉掺入混凝土后,对混凝土力学、热学、变形及耐久性的影响。最后,对磨细石灰岩石粉的运用前景进行了初步经济效益分析。

侵蚀性流体作用下石灰岩渗透性变化规律

为研究侵蚀性流体渗透过程中完整石灰岩石渗透性的变化规律,设计3组不同的渗透溶液化学侵蚀条件和应力条件下的石灰岩芯渗透实验,通过测量每种工况下不同时刻渗出液流量、渗出液中含有的离子浓度等数据,分析完整石灰岩渗透特性的主要影响因素和演化机理。实验结果表明:渗透液体侵蚀和应力施加对岩石渗透性演变存在不同作用。由于加压(围压、轴压、渗透压)对岩芯渗透性具有时效性,在实验初期(0~50 h)3种工况下岩芯渗透率都急剧下降,应力作用是引起岩石渗透率变化的主要因素;随着实验过程的进展,岩芯内部孔隙喉道逐渐闭合,大约50 h之后,渗透流体的化学侵蚀作用开始显现,在之后的330 h中,渗透液为蒸馏水时岩芯渗透率基本趋于稳定,渗透溶液为p H=6的硫酸钠溶液或硫酸溶液时岩芯渗透率则持续下降,表明实验后期渗透液的化学侵蚀作用对岩芯渗透率演变起主要作用。3种工况实验过程中岩芯渗出液中始终有离子溶出,但是不同的渗透液体对岩芯矿物质的溶解效果有差异,显著改变渗出液的离子浓度和离子浓度比值。当渗透溶液中存在促进矿物质溶解的成分并且渗透压力较小时,渗透液中离子逐渐积累变多但不能及时被运移到岩芯外,从而可能产生沉淀堵塞岩芯渗透通道。实验过程中,完整石灰岩石渗透性的演变特性是渗透溶液的侵蚀作用、应力作用和溶质运移沉淀共同作用的结果。

石粉对水泥湿堆积密度和混凝土性能的影响

石灰岩机制砂的用量越来越大,相应地,它的副产物石灰岩石粉也越来越多。如果不能合理地将石粉加以利用,势必给环境造成很大的负担。以石粉做矿物掺合料取代水泥为研究目的,对比了在0%、10%、15%、20%时的比例等质量取代水泥,对混凝土工作性能、抗压强度和抗渗性能的影响,得出石粉取代水泥的比例为10%左右时,对混凝土的性能有较好的改善作用。通过测其石粉和水泥混合后的湿堆积密度,得出石粉的质量比为10%时,二者的密实度最大。表明石粉做掺合料时,可通过二者混合后密实度的变化来判断二者的最佳比例。

不同岩性的石粉作掺合料对混凝土性能的影响

该文利用人工砂生产中产生的石灰岩石粉与大理石粉、花岗岩石粉以及粉煤灰作为混凝土掺合料,对各种掺合料拌制的混凝土进行性能比较研究。试验结果表明:石灰岩石粉能提高混凝土拌合物的扩展度、塌落度,降低泌水率,改善混凝土工作性能,可提高混凝土的早期强度,且后期强度也与粉煤灰混凝土相近,有利于提高混凝土的抗碳化性能,但其混凝土的抗氯离子渗透性能差于粉煤灰混凝土。

石灰岩机制砂中石粉作掺合料对混凝土工作性和强度的影响

在利用岩石轧制生产机制砂的过程中，伴随产生相当数量的岩石细粉副产物。为了有效利用石粉资源，本文对石灰岩石粉代替粉煤灰作混凝土矿物掺合料的可用性进行了研究。首先，测试了掺入石粉的水泥胶砂的流动性和力学性能；其次，对石粉取代粉煤灰作掺合料对C30、C60、C80机制砂混凝土工作性和强度的影响进行了试验和讨论。结果显示：在混凝土中掺入15％～22．5％数量的石粉作掺合料是完全可行的，其对混凝土强度的影响基本相当于等掺量的粉煤灰。

骨料含粉对水泥基材料作用效应研究

掺石灰岩所含石粉的水泥砂浆抗压强度为评价指标,以惰性石英岩石粉为基准,采用现象学研究方法解耦了石灰岩含粉在水泥基材料中的稀释效应、级配效应和异质成核效应。研究结果表明:稀释效应随石灰岩石粉掺量的增大线性增大,级配效应随其细度的增大变化较小,其对于水泥基材料的强度发展属于次要因素,石灰岩石粉异质成核效应随其掺量增大呈先增大后减小的规律,随水泥水化龄期的增大逐渐减小。异质成核效应最大时,水泥-石灰岩石粉胶凝体系达到最优配合比,即异质成核效应决定了石灰岩石粉的最佳掺量。

Effect of Perched Water Tables on Aluminosilicate Stability and Soil Genesis

The mineral stability and solute activities of soil solution extracted from selected horizons of seven studied pedons of Alfisols in Kentucky, USA, and the relationship between distribution of iron-manganese concretions and the restrictive layers were investigated. The results showed that the genesis and development of these soils and mineral weathering trends were strongly influenced by the depth of bedrock and the presence of perched water tables at lithic (limestone) interfaces due to the dissolution and buffering effect of limestone bedrock. The extractable Mg/Ca ratio as depth function and soil depth above bedrock could be used as indices of weathering and degree of soil development. Maximum iron-manganese concretion accumulation was found to occur in the horizon overlying clay horizon (>40% clay) with a sharp increase in clay content (>10%), which suggested that zones of Fe-Mn concretion accumulation in soils of the Inner Bluegrass Region appeared to be a sensitive genetic indicator of argillic horizons with restrictive permeability.

Characteristics and distributions of humic acids in two soil profiles of the southwest China Karst area

Characteristics and distributions of humic acid(HA) and soil organic matter(SOM) in a yellow soil profile and a limestone soil profile of the southwest China Karst area were systematically investigated to reveal their evolutions in different soils of the study area. The results showed that characteristics and distribution of SOM along the two soil profiles were notably different. Total organic carbon(TOC) contents of soil samples decreased just slightly along the limestone soil profile but sharply along the yellow soil profile. TOCs of the limestone soils were significantly higher than those of the corresponding yellow soils, and C/N ratios of SOMs showed a similar variation trend to that of TOCs, indicating that SOM can be better conserved in the limestone soil than in the yellow soil. The soil humic acids were exhaustively extracted and further fractionated according to their apparent molecular weights using ultrafiltration techniques to explore underlying conservation mechanisms. The result showed that C/N ratios of HAs from different limestone soil layers were relatively stable and that large molecular HA fractions predominated the bulk HA of the top soil, indicating that HA in the limestone profile was protected while bio and chemical degradations were retarded. Combined with organic elements contents and mineral contents of two soils, weconcluded that high calcium contents in limestone soils may play a key role in SOM conservation by forming complexation compounds with HAs or/and enclosing SOMs with hypergene CaCO_3 precipitation.

Comparative Study on Debris Flow Initiation in Limestone and Sandstone Spoil

Large spoil tips from reconstruction works as a result of the Wenchuan Earthquake in China are new debris flow hazards to the human society.However,there is a lack of detailed comparative study on debris flow initiation in different spoil materials.This paper describes a series of tests and analyses on debris flow characteristics(initiation,scale and mechanism) at six sites with limestone and sandstone materials near the Dujiangyan area.Research shows the limestone spoil contains debris flow prone clay content with high concentration of montmorillonite(highly expandable).In addition,limestone spoil is of such a low permeability that water mainly concentrates in the upper surface layer.Those factors make it easy for the increase of pore water pressure,decline of internal friction and conhesion force,leading to the occurence of large debris flows.In contrast,the sandstone spoil is less problematic and causes no major debris flow threats.Based on our research on the mechanism,the"stereometric drainage"method is sucessfully applied to control limestone spoil debris flows.

The Effect of Tree Species on the Chemical Properties of Soil in the Rehabilitation of a Limestone Quarry at Athi River, Kenya

A comparison of field performance of Acacia xanthophloea, Schinus molle, Casuarina equisetifolia and Gravellia robusta plant species was made in an exhausted limestone quarry, backfilled with limestone mine waste in a semi-arid area in Athi River, Kenya. The aim of the study was to determine if the tree species had an influence on the soil chemical properties. The soil had alkaline pH ranging from 8.0 to 8.98, low nitrogen content （〈 0.03%）, moderate phosphorus concentrations ranging from 44.15 ppm to 21.33 ppm and high to moderate exchangeable cations （Na, Ca, Mg and K）. All the tree species exerted a positive influence on soil properties necessary for plant growth. The pH values and total phosphorus were relatively lower in soils close to the trees （0.5 m） and increased with distance from the trees, while the soil values for total nitrogen and exchangeable cations were relatively higher close to the trees. C. equisetifolia had the best growth performance and a higher positive influence on the soil chemical properties necessary for plant growth followed by A. xanthophloea. It was concluded that trees should remain a feature of quarry rehabilitation because of their role in maintaining the biophysical environment.

Effects of Limestone Powder on Rheological Properties of Cement - Fly Ash Mortar

This article studies the effects of limestone powder on rheological properties of cement - fly ash mortar with RHEOLAB QC type rotation viscometer. The Bingham fluid model is introduced to fit the yielding stress and plastic viscosity of the mortar. The POWER LAW fluid model is introduced to fit the rheological index of the mortar. The results show that, adding limestone powder and fly ash to the cement mortar significantly decreases the yield stress of the mortar, changes the plastic viscosity of the mortar, increases the rheological index, decreases the degree of shear thinning of the mortar, and thereby improves the mortar＇ s workability. In the case of cement - fly ash mortar, with the increase of limestone powder content, both the yield stress and plastic viscosity of the mortar increase. When the limestone powder content is not higher than 14%, the increase of yield stress is not significant. When the limestone powder content is lower than 8%, the increase of plastic viscosity is not significant. When the content of limestone powder is higher than 22%, the rheological index of the mortar decreases and the degree of shear thinning increases. The effects of limestone powder＇ s packing density, shape and size, specific surface area, and fluid volume, are found to be the four major factors responsible for the changes ofrheological properties of the mortar.

Origin of the Furongian limestone breccias in the North China Platform

Limestone breccias are a common phenomenon in the Cambrian successions worldwide. They bear important geological im- plications that have attracted geologists for several decades. There are, however, still controversies on their origins, especially those of the breccias with abundant vertically orientated clasts. The Furongian （upper Cambrian） Chaomidian Formation of the North China Platform contains numerous levels of limestone breccias and conglomerates that provide an excellent example to look into their formative processes. These breccias and conglomerates have been the focus of study and discussion since the 1980s, but yet there is still no consensus with respect to their geneses. Recently, Van Loon and others argued that the vertically orientated clasts of the breccias developed by a number of simultaneous ＂fountains＂ on the paleo-seafloor; the ＂fountains＂ formed by upward-directed fluidized flows originated from the sediment underlying the brecciated limestones. While the novel ＂fountain＂ hypothesis is not impossible, based on field evidences and theoretical considerations, however, it is most likely that the vertically orientated clasts resulted from their re-orientation by gillaceous sediment that was interbedded with brecciated limestone took place under shallow burial. upward flow of thixotropically liquidized, uncemented ar- fragments. Besides, the deformation processes most likely

Bio-Fertilizer,Ground Magnesium Limestone and Basalt Applications May Improve Chemical Properties of Malaysian Acid Sulfate Soils and Rice Growth

Acid sulfate soils are normally not suitable for crop production unless they are appropriately ameliorated. An experiment was conducted in a glasshouse to enhance the growth of rice, variety MR219, planted on an acid sulfate soil using various soil amendments.The soil was collected from Semerak, Kelantan, Malaysia. Ground magnesium limestone(GML), bio-fertilizer, and basalt(each 4t ha-1) were added either alone or in combinations into the soil in pots 15 d before transplanting. Nitrogen, P and potash were applied at 150, 30, and 60 kg ha-1, respectively. Three seven-day-old rice seedlings were transplanted into each pot. The soil had a p H of 3.8 and contained organic C of 21 g kg-1, N of 1.2 g kg-1, available P of 192 mg kg-1, exchangeable K of 0.05 cmol c kg-1,and exchangeable Al of 4.30 cmol c kg-1, with low amounts of exchangeable Ca and Mg(0.60 and 0.70 cmol c kg-1). Bio-fertilizer treatment in combination with GML resulted in the highest p H of 5.4. The presence of high Al or Fe concentrations in the control soil without amendment severely affected the growth of rice. At 60 d of growth, higher plant heights, tiller numbers and leaf chlorophyll contents were obtained when the bio-fertilizer was applied individually or in combination with GML compared to the control. The presence of beneficial bacteria in bio-fertilizer might produce phytohormones and organic acids that could enhance plant growth and subsequently increase nutrient uptake by rice. Hence, it can be concluded that addition of bio-fertilizer and GML improved rice growth by increasing soil p H which consequently eliminated Al and/or Fe toxicity prevalent in the acid sulfate soil.