The influence of binder/aggregate ratio on the pore properties and strength of repair mortars

Repair mortars with different B/Ag (binder/aggregate) ratios and natural stone were studied in order to understand the influence of limestone aggregate on the properties of mortar and to check the compatibility of repair mortar with a porous limestone. Three different types of mortars with three different aggregate contents were evaluated by using mercury intrusion porosimetry (MIP) and water saturation method (WSM). Changes in density and uniaxial compressive strength as a function of aggregate content were also recorded. For comparison the properties of the porous limestone were also tested, since it is used in monuments and also as aggregate in the mortar. Tested mortars had average porosities of 27.0 % (±2.0), while oolitic limestone has higher average porosity of 32.2 % (±1.9). The limestone has mainly medium and large pore radii (1–100 μm) while the repair mortars even with high aggregate content has predominantly smaller pores. All but one pure repair mortars have higher uniaxial compressive strength than that of the oolitic limestone. The strength decreases while porosity increases with increasing aggregate content.     

Experimental investigations on the elastic parameters and uniaxial compressive strength of slate under freeze–thaw cycles

ABSTRACT

In this study, uniaxial compression experiments with seven different bedding angles and six numbers of freeze–thaw cycles were conducted to investigate the influences of freeze–thaw cycles on the elastic parameters and the uniaxial compressive strength of slate. The laws of the elastic parameters, uniaxial compressive strength and failure characteristics were analysed, and a new uniaxial compressive strength prediction model that considers the bedding angle and the number of freeze–thaw cycles as control variables was established and verified using the experimental data. The results showed that the uniaxial compressive strength, elastic modulus and shear modulus decreased exponentially with an increasing number of freeze–thaw cycles. However, the Poisson’s ratio increased linearly with an increasing number of freeze–thaw cycles. The uniaxial compressive strength initially decreased and then increased with increasing bedding angle. There are three forms of failure occurred during the tests: when the bedding angle was 0°≤β ≤ 26.6°, the splitting failure and shear failure occurred at the same time; when the bedding angle was 26.6°≤β ≤ 83.0°, sliding failure occurred along the bedding plane; and when the bedding angle was 83.0°≤β ≤ 90°, splitting failure occurred along the axial direction of sample.     

Experimental study on mechanical properties of granite after freeze–thaw cycling

It is important to understand the effect of freeze–thaw cycles on the mechanical properties of rocks. In this paper, the variation of the uniaxial compressive strength, peak strain, elastic modulus and stress–strain curves of granite subjected to freeze–thaw cycles with different heating temperatures were studied experimentally and the relationships were derived. As the number of freeze–thaw cycles increases, the compressive strength and elastic modulus decrease, while the peak strain decreases. In addition, an increased temperature increases the peak strain while decreasing the compressive strength and elastic modulus. An expression for the initial damage for the adopted rock material due to freeze–thaw cycling was proposed based on the Loland model. The current research has established a solid foundation for further experimental studies on the fatigue behavior of granite after freeze–thaw cycling.     

冻融条件TG固化剂石灰土基层性能研究

为了进一步研究TG固化剂石灰土在冻融条件下的各项性能, 分别对TG固化剂石灰土进行冻融作用前后的无侧限抗压强度试验和劈裂试验以及干缩试验. 结果表明: 随着冻融循环次数的增加, 无侧限抗压强度以及劈裂强度逐渐减小, 经历8次冻融循环以后强度衰减达到最大值. 经过冻融循环作用后试件的无侧限抗压强度以及劈裂强度残留值随着含水率和压实度的增加而增加, 通过冻融试验得到的抗冻性能指标BDR值在51%以上, 与未饱水冻融循环得到的最终残留强度值保持一致. 经冻融循环作用后TG固化剂石灰土的干缩应变和干缩系数减小, 干缩性能有所提高. 冻融循环条件下TG固化剂石灰土抗冻性能良好, 可以应用于路面基层.     

Assessment of the Effects of Freeze–Thaw and Salt Crystallization Ageing Tests on Anahita Temple Stone,Kangavar, West of Iran

Building stone of Anahita Temple seriously suffers from weathering due to long term freezing-thawing and salt crystallization processes. This article investigates possible changes of physical and mechanical characteristics of this stone subjected to freeze–thaw and salt crystallization ageing tests. Fresh samples obtained from the Chelmaran quarry (the main quarry supplying for Anahita Temple stone) were tested under freeze–thaw and salt crystallization experiments. The freeze–thaw and sodium sulfate salt crystallization are suggested to be the most effective factors affecting in apparent deterioration of the stone in compare to the magnesium sulfate salt crystallization test. Significant decreases in mechanical properties of the stone were observed after freeze–thaw and salt crystallization tests. However, more mechanical losses were recorded after the salt crystallization cycles than the freeze–thaw cycles. This is probably due to crystallization pressure of salt crystals in compare to ice wedging force, which promoted more development of micro-fractures in the specimens. Probably, intrinsic factors of the stone such as frequent calcite veins and stylolites, are the main factors that control the durability of Anahita Temple stone. Preferential weakening along these features during freeze–thaw and salt crystallization cycles led to physical destruction and strength loss of the stone. Based on comparison between experimentally induced damages and field observations, reasonably freeze–thaw process is major factor in weathering of Anahita Temple stone. It should be noted that recorded 102 frozen days for the region imply high destruction potential of the stone during freeze–thaw cycles.     

Interactions between freeze–thaw actions,wind erosion desertification,and permafrost in the Qinghai–Tibet Plateau

The unique natural environment of the Qinghai–Tibet Plateau has led to the development of widespread permafrost and desertification. However, the relationship between desertification and permafrost is rarely explored. Here we study the interaction between desertification and permafrost using a combination of simulations, experiments, and field observations in the Qinghai–Tibet Plateau. Results show the cohesion values of the test samples that experienced 1, 3, and 6 freeze–thaw cycle times decreased by 65.9, 46.0, and 35.5 %, respectively, and the compressive strength of the test samples decreased by 69.6, 39.6, and 34.7 %, respectively, compared to the test samples that did not experience freeze–thaw cycles. The wind erosion rate of the test block eroded by sand-bearing wind was far larger than that by clean wind under the same conditions; the maximum value was 50 times higher than that by clean wind. The wind erosion rate increased with an increasing number of freeze–thaw cycles, water content, and freeze–thaw temperature difference. The ground temperature below the sand layer was decreased, compared to the natural ground surface that without sand layer covering, the drop amplitude of yearly average temperature was roughly maintained at 0.2 °C below the thick sand layer (1.2 m), and the maximum drop of yearly average temperature was 0.7 °C below the thin sand layer (0.1 m). Therefore, with the presence of water, the destruction of surface soil structure caused by repeated and fierce freeze–thaw actions is the main cause of wind erosion desertification in the permafrost region of Qinghai–Tibet Plateau, and sand-bearing wind is the main dynamic force. The development of eolian sand deposits after the desertification emerges. As a result, the properties of the underlying surface are altered. Due to the high reflectivity and poor heat conductivity of the sand layer, the heat exchange of the land–atmosphere system is impeded, causing a drop in the ground temperature of the underlying permafrost that subsequently preserves the permafrost.     

Physical weathering of building stones induced by freeze–thaw action: a laboratory long-term study

Damages to natural building stones induced by the action of frost are considered to be of great importance. Commonly, the frost resistance of building stones is checked by standardised freeze–thaw tests before using. Corresponding tests normally involve 30–50 freeze–thaw action cycles. In order to verify the significance of such measurements, we performed long-term tests on four selected rocks over 1,400 freeze–thaw action cycles. Additionally, numerous petrophysical parameters were analysed to compare the behaviour of rocks in the weathering tests according to the current explanatory models of stress formation by growing ice crystals in the pore space. The long-term tests yield more information about the real frost sensibility of the rocks. A clear deterioration cannot be determined in most cases until 50 weathering cycles have been completed. In the freeze–thaw tests, the samples are also stressed by changing temperature and moisture, indicating that different decay mechanisms can interfere with each other. Thus, thermohygric and moisture expansion are important damage processes.     

冻融循环对固化铅污染土强度与孔隙特征影响的试验研究

水泥基固化剂封闭是近年来重金属污染修复治理的主要技术手段之一。冻融循环作用是影响水泥固化重金属污染土力学特性的重要外营力。本文以人工制备的铅污染土为研究对象,结合冻融实验和室内土工试验,研究冻融循环作用对铅污染土无侧限抗压强度的影响。结果表明:随着水泥掺量的增大,水泥固化铅污染土的无侧限抗压强度增大,破坏应变减小;随着铅离子掺量的增大（污染程度升高）,水泥固化铅污染土的无侧限抗压强度q_u降低,应力-应变曲线变化趋势更加相似;水泥固化铅污染土的无侧限抗压强度q_u随冻融频次的增大而降低;相同冻融频次条件下,随着水泥掺量的增加,水泥固化铅污染土的无侧限抗压强度q_u损失率降低。基于SEM图像对固化铅污染土进行微观结构定量分析,表明随着冻融次数的增加,试样中细颗粒（< 1 μm）和细孔隙（< 2 μm）所占比例均提高。冻融作用对土体结构的破坏可能是导致土样无侧限抗压强度q_u降低的主要原因。     

Water absorption process effect on strength of Ayazini tuff,such as the uniaxial compressive strength (UCS), flexural strength and freeze and thaw effect

Tuffs have been used as a construction material possibly since ancient times. In Afyonkarahisar, Turkey, there are numerous buildings constructed by tuff. Tuff has been a local construction material, during the Roman, Seljuk and Ottoman periods. Even though tuffs have relatively low durability and low strength values compared to marble, etc., they have survived with no major deterioration failures on many historical buildings. It has also been preferred because of its high porous texture, lightweight and easy shaping and process properties in the building sector. Naturally, it would be easily affected by water and humidity because of its porous structure. However, having this kind of structure leads to poor durability properties due to keeping water in it. The main objective of this study was to evaluate the physical and mechanical properties of the tuff quarried from the region and possible water effect, which may lead to degradation of its strength and durability of the material, thereby shortening the life span of the building structure used. Samples, which were tested after exposing to water and the freeze and thaw effects, were measured at a certain time. In this study, uniaxial compressive strength and flexural strength tests were conducted on test samples. The test results indicate that water may deteriorate the tuff’s strength properties and durability of the materials in due time.     

Evaluation of the physico-mechanical parameters affecting the deterioration rate of Ahlat ignimbrites (Bitlis,Turkey)

The paper principally focuses on the durability assessment of various stratigraphic levels of Ahlat ignimbrites collected from the eastern region of Turkey. A total of four different ignimbrite types with dissimilar color, texture and particularly welding degree were tested in laboratory. The laboratory tests performed on the ignimbrite specimens indicate that the welding degree as well as the lithic material content mainly controls the strength and capillarity properties of the ignimbrites. In addition, the durability of highly porous ignimbrites strongly depends upon the degree of welding. The effect of several weathering agents on the ignimbrites was evaluated on the basis of decay constant parameter. Accordingly, salt and ice crystallization pressures are a couple of major destructive agents acting within the micropores of the ignimbrites. Conversely, the investigated specimens are relatively durable against cyclic wetting–drying. Statistical evaluations reveal that the pore diameter is the major controlling factor on the deterioration rate of the ignimbrites after specifically recurrent freeze–thaw cycles. Moreover, the dry unit weight of the ignimbrites is more significant than the uniaxial compressive strength considering the deterioration rates during wetting–drying and salt crystallization. A less significant relationship was obtained between pore diameter and salt crystallization decay constant.     

Study on frost resistance of rapid-hardening magnesium phosphate-ferro-aluminate composite cement北大核心CSCD

随着冬季抢修抢建混凝土工程的增多,研发适用于严寒地区具有良好抗冻性的快硬水泥意义重大。磷酸镁水泥具有早期强度高、初凝时间短、与混凝土相容性好等特点,被视为混凝土工程的良好快修快建材料。然而,磷酸镁水泥制备的水泥砂浆或混凝土在北方地区的冬季往往会受到冻融循环作用,导致其耐久性和强度出现不同程度的退化。为增强磷酸镁水泥的抗冻性,在磷酸镁水泥制备中用铁铝酸盐水泥代替一定数量的过烧氧化镁,制备出快硬磷酸镁-铁铝酸盐复合水泥。通过冻融循环前后磷酸镁-铁铝酸盐复合水泥砂浆试件的质量损失测试、强度试验、孔隙率测试及SEM-EDS测试,得出：铁铝酸盐水泥代替氧化镁的数量在30%~40%时,制备的磷酸镁-铁铝酸盐复合水泥砂浆试件冻融循环后的质量损失率最小,抗压强度和抗折强度达到峰值,抗压强度和抗折强度剩余率最高,孔隙率最小,因而该配合比的磷酸镁-铁铝酸盐复合水泥具有最好的抗冻性。由SEM-EDS测试可知磷酸镁水泥砂浆试件冻融循环后,基体中的胶凝材料K-鸟粪石部分溶解,试件整体结构疏松,晶体间存在大量间隙;磷酸镁水泥制备中掺入铁铝酸盐水泥后,制得的磷酸镁-铁铝酸盐复合水泥水化生成大量晶体填充于砂浆试件基体内部,无定形水化产物对砂浆试件的强度有一定补偿作用,使得磷酸镁-铁铝酸盐复合水泥砂浆试件在冻融循环后孔隙率大幅减小,密实度得到提高,使得磷酸镁-铁铝酸盐复合水泥的抗冻性能得到了显著增强。磷酸镁-铁铝酸盐复合水泥为北方严寒地区冬季混凝土抢修抢建工程提供了一种新材料。     

Permeability and P-wave velocity change in granitic rocks under freeze–thaw cycles

An extensive experimental investigation of microstructural changes in granites under freeze–thaw cycles using permeability and P-wave velocity measurements is described. Two types of natural granite rocks are considered and tested under dry and saturated conditions. The specimens were subjected to 200 heating–cooling cycles (??20°C/?+?20°C); each cycle had a duration of 24 h. The results indicate that the ageing process decreases the permeability and the P-wave velocity. The reduction in P-wave velocity is likely to be due to microcrack development (material damage). In dry samples, the microcracks result from the repeated differential contraction–dilatation of the mineral components. In water-saturated samples, there is an additional effect of freezing and thawing of water in the porous network. The decrease in permeability in the dry samples is due to partial closure of existing microcracks. In water-saturated samples, there was no increase in the permeability. A physically acceptable explanation is that new microcracks are not necessarily connected with those that already exist. Therefore the physicochemical process resulting from water–rock interactions also affects the permeability. This phenomenon reduces fluid flow in the material.     

冻融循环对砼护坡界面抗剪强度影响试验研究

以混凝土铰接块+土工布+黏土护坡结构室内模型为研究对象, 分别讨论不同含水量及冻融循环次数下接触面间抗剪强度指标的变化规律. 分别测定常温下护坡结构含水量在15.7%~28%之间的黏聚力(C)和内摩擦角(φ)值, 含水量为18%以及饱和状态下经过10次冻融循环的C值和φ值, 采用多元回归法进行分析. 结果表明: 含水量对护坡结构的抗剪强度指标弱化十分明显, 斜面摩擦试验中黏聚力和内摩擦角均随含水量增加而降低; 含水量与内摩擦角呈线性相关关系, 与黏聚力呈乘幂关系. 冻融循环过程水分迁移导致砼护坡界面水分增大, 界面抗剪强度指标弱化. 随冻融循环次数的增加砼铰接块护坡界面的抗剪强度减小, 对于非饱和黏性土, 在5次冻融循环时减小幅度较大, 但10次冻融循环时减小幅度较小并基本趋于稳定; 而对于饱和黏性土, 其抗剪强度指标随冻融循环次数的增加减小幅度并不明显.     

冻融循环对石灰处置粉质黏土静强度影响研究

以吉林－荒岗高速公路沿线的粉质黏土为研究对象,对不同石灰掺入比的土样试件进行0、2、4、6、8、10、12次冻融循环试验。通过室内静三轴试验,研究了冻融循环作用对石灰处置粉质黏土强度的影响。研究结果表明,石灰处置粉质黏土的应力-应变关系曲线呈应变软化型,峰值强度随围压增大而升高,粉质黏土峰值强度降低幅度值比石灰处置粉质黏土峰值强度降低幅度值大,经历4次冻融后应力-应变曲线峰值强度趋于稳定;冻融作用后石灰处置粉质黏土抗剪强度衰减率比粉质黏土的抗剪强度衰减率小,抗剪强度随围压的升高而增大;同一围压条件下石灰处置粉质黏土弹性模量随着冻融次数增加逐渐减小,经历4次冻融后基本趋于稳定。     

A Study of the Impacts of Freeze–Thaw on Cliff Recession at the Calvert Cliffs in Calvert County,Maryland

The Calvert Cliffs, which form much of the western coastline of the Chesapeake Bay in Calvert County, Maryland, are actively eroding and destabilizing, yielding critical situations for many homes in close proximity to the slope’s crest. Past studies have identified that waves directly interacting with the slope toe control cliff recession; however, where waves do not regularly interact with the slope toe, freeze–thaw controls recession. This study investigated the validity of this second claim by analyzing the recession rate and freeze–thaw behavior of six study sites along the Calvert Cliffs that are not directly affected by waves. While waves do remove failed material from the toe in these regions, freeze–thaw is believed to be the dominant factor driving recession at these sites. Past recession rates were calculated using historical aerial photographs and were analyzed together with a number of other variables selected to represent the freeze–thaw behavior of the Calvert Cliffs. The investigation studied sixteen independent variables and found that over 65 % of recession at these study sites can be represented by freeze–thaw through the following variables: (1) slope aspect, (2) soil freeze–thaw susceptibility, (3) the number of freeze–thaw cycles, and (4) the weighted shear strength. Future mitigation techniques at these sites should focus on addressing these variables. Unmitigated, the Calvert Cliffs will continue to recede until a stable slope angle is reached and maintained.     

Experimental investigations on the influence of cyclical freezing and thawing on physical and mechanical properties of saline soil

Uniaxial compressive strength experiments were performed on saline loess different water and salt contents, and multiple freeze/thaw cycles at room temperature. The experiments revealed changes to the stress–strain curve and the failure mode of the saline loess. The results indicated that soil strength is intensified or weakened during freezing and thawing due to the injection of sodium sulfate solute. Cyclical freezing and thawing is a process to get a new dynamic equilibrium, and under these experimental conditions, six freeze–thaw cycles are need for loess with sodium sulfate to reach a new dynamic equilibrium.     

冻融循环影响风化砂改良膨胀土抗剪强度室内试验研究

本文以三峡库区广泛分布的风化砂来改良膨胀土,通过在膨胀土中掺入10%、20%、30%、40%、50%的风化砂,进行1、3、6、9、12次冻融循环,最后对不同冻融循环次数作用后改良膨胀土制备样进行直接剪切试验,测定不同掺砂量及不同冻融次数下,各试样的强度参数,得出冻融循环对风化砂改良膨胀土抗剪强度指标及强度规律的影响.试验结果表明:在同一掺砂比例下,风化砂改良膨胀土的抗剪指标和抗剪强度随冻融循环次数的增大而减小,最后逐渐趋于稳定,其中黏聚力与冻融循环次数呈对数关系; 在同一冻融循环次数下,黏聚力随掺砂比例的增大而减小,内摩擦角随掺砂比例的增大而增大.     

Relationship between density,compressive strength,tensile strength and aggregate properties of andesites from Hungary

Aggregate properties and strength parameters of four andesites from two operating Hungarian quarries of Nógrádkövesd (one lithotype) and Gyöngyössolymos (three lithotypes) are presented in this paper. Air-dry, water-saturated and freeze–thaw subjected specimens were tested on core-drilled cylindrical specimens, and the aggregate properties were also determined from the remaining part of the drilled rock blocks. Tensile strength values rapidly decreased from air-dry to water-saturated and finally to freeze–thaw subjected specimens. Linear relationships between air-dry and water-saturated bulk densities and between UCS and modulus of elasticity were found. Micro-fabric influences strength and aggregate parameters of studied andesites; fine porphyritic andesite has the highest UCS and tensile strength and the best micro-Deval results, while coarser porphyritic andesite has lower strength and aggregate parameters. Test results were compared with previously published rock mechanical data of intermediate and basic igneous rocks. A good exponential correlation was found between micro-Deval and UCS values of this paper and previously published data sets, but there was no indication that micro-Deval values correlate well with Los Angeles values.     

Hydro-mechanical evaluation of stabilized mine tailings

. In this study, mine tailings waste was stabilized using a combination of lime, fly ash type "C", and aluminum. Treated samples were subjected to mineral identification for evaluating the formation of ettringite and gypsum. Also, unconfined compression, hydraulic conductivity, and cyclic freeze and thaw tests were performed to evaluate the hydro-mechanical properties of the stabilized samples. Experimental results have shown that the application of lime and fly ash type "C" to high sulfate content tailings has improved its plasticity, workability, and volume stability. Moreover, upon addition of aluminum to lime and fly ash in a sulfate-rich environment, ettringite and calcium sulfo-aluminate hydrate are formed in these samples. Application of 5% lime, 10% fly ash type "C", in combination with 110 ppm aluminum, resulted in the formation of a solid monolith capable of producing more than 1,000 kPa of unconfined compressive strength, and reduced tailings permeability to 1.96᎒^–6 cm s^–1, which is less than the recommended permeability of 10^–5 cm s^–1 by most environmental protection agencies for reusability of solidified/stabilized samples. The permeability of the treated tailings samples remained below the recommended permeability, even after exposing the treated samples to 12 freeze and thaw cycles. Therefore, based on the experimental results, it is concluded that treatment of high sulfate-content tailings with lime and fly ash, combined with the availability of aluminum for reactions, is a successful method of solidifying highly reactive mine tailings.     

Typical Soft–Sediment Deformation Structures Induced by Freeze/Thaw Cycles: A Case Study of Quaternary Alluvial Deposits in the Northern Qiangtang Basin, Tibetan Plateau

With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at Dogai Coring, northern Qiangtang Basin, Tibetan Plateau. Deformation is present in the form of plastic structures(diapirs, folds and clastic dykes), brittle structures(micro–faults) and cryogenic wedges. These soft–sediment deformation features(except the micro–faults) are mainly characterized by meter–scale, non–interlayered, low–speed and low–pressure displacements within soft sediments, most commonly in the form of plastic deformation. Taking into account the geographic setting, lithology and deformation features, we interpret these soft–sediment deformation features as the products of freeze/thaw cycles, rather than of earthquake–induced shock waves, thus reflecting regional temperature changes and fluctuations of hydrothermal conditions in the uppermost sediments. The micro–faults(close to linear hot springs) are ascribed to regional fault activity; however, we were unable to identify the nature of the micro–faults, perhaps due to disturbance by subsequent freeze/thaw cycles. This study may serve as a guide to recognizing the differences between deformation structures attributed to freeze/thaw cycles and seismic processes.