Assessing the environmental performance of stabilised rammed earth walls using a climatic simulation chamber

The SHU climatic simulation chamber is a novel piece of apparatus that allows testing of full-sized walls with realistic inner and outer wall climatic conditions. Four SRE test walls were successfully constructed and tested over four separate regimes to measure physical properties such as pressure-driven moisture ingress, rate of moisture penetration, and internal/interstitial condensation. The walls far exceeded a series of cyclic pressure-driven rainfall penetration tests based on BS 4315-2. After 5 days of exposure to static pressure-driven moisture ingress there was no evidence of moisture penetration or erosion. The embedded sensor array detected no significant increase in the relative humidity or liquid moisture content inside the test walls, throughout a range of temperature differentials with high levels of humidity, indicating a negligible risk of internal or interstitial condensation.     

浅析夯土建筑材料的耐久性

针对夯土建筑的历史和夯土建筑所用夯土材料的力学性质、耐久性质以及夯土材料的改性问题进行了研究,以期更好地推广夯土这种生态环保的建筑材料和唤起人们对夯土建筑的重视。     

夯土建筑土料工程特性的试验研究

通过击实试验、直接剪切试验和轴向抗压试验得到了3种夯土建筑土料的压实性、抗剪强度、抗压强度等工程特性指标,可作为夯土建筑设计的技术参考指标,为编制村镇夯土建筑规范提供基础资料。     

Embodied energy in cement stabilised rammed earth walls

Rammed earth walls are low carbon emission and energy efficient alternatives to load bearing walls. Large numbers of rammed earth buildings have been constructed in the recent past across the globe. This paper is focused on embodied energy in cement stabilised rammed earth (CSRE) walls. Influence of soil grading, density and cement content on compaction energy input has been monitored. A comparison between energy content of cement and energy in transportation of materials, with that of the actual energy input during rammed earth compaction in the actual field conditions and the laboratory has been made. Major conclusions of the investigations are (a) compaction energy increases with increase in clay fraction of the soil mix and it is sensitive to density of the CSRE wall, (b) compaction energy varies between 0.033 MJ/m³ and 0.36 MJ/m³ for the range of densities and cement contents attempted, (c) energy expenditure in the compaction process is negligible when compared to energy content of the cement and (d) total embodied energy in CSRE walls increases linearly with the increase in cement content and is in the range of 0.4-0.5 GJ/m³ for cement content in the rage of 6-8%.     

纤维加筋土坯的蒸发过程及抗拉强度特性

土坯作为一种生态、低碳和环保的建筑材料,其力学性能是学界和工程技术人员关注的重点.为了提高土坯的综合抗拉特性,提出采用纤维加筋技术对土坯进行改性处理.通过模拟土坯的形成过程,制备了一系列不同纤维掺量(0～0.2％)、初始含水率(16.5％～20.5％)和干密度(1.50～1.70 g/cm3)的压实土坯试样,进行自然干...     

Compressive strength characteristics of cement stabilized rammed earth walls

In order to minimize the environmental impacts caused by over exploitation of natural resources for the production of building material, the possibility of using cement stabilized rammed earth for load-bearing walls has been assessed. Since the vertical load carrying capacity primarily depends on the compressive strength, a comprehensive study was conducted for rammed earth walls constructed with three commonly available laterite soil types in Sri Lanka. The results indicate the possibility of using rammed earth for single storey houses which may also be extended to two storey houses. The load deformation characteristics were used to determine the suitable partial safety factors for the structural design.     

夯土民居生土墙体材料改性实验初探

对目前常用的生土化学和物理改性方法进行了归纳分析,以素土和矿粉为对比组,利用碱性激发剂加入对比组对其潜在活性进行激发,并给对比组加入剑麻纤维分别进行抗折、抗压试验,结果表明矿粉和剑麻纤维可用于陕南生土建筑的改性。     

First exploratory study on dynamic characteristics of rammed earth buildings

Rammed earth construction is attracting a renewed interest throughout the world thanks to its “green” characteristics in the context of sustainable development. Several studies have been carried out to investigate this material and evaluate its durability along with its mechanical, thermal and earthquake capacities. This paper presents a study on the parameters needed for the seismic design of rammed earth buildings in accordance with current earthquake standards. First, the dynamic parameters of buildings such as natural frequencies and damping ratios-which were necessary to determine the equivalent static seismic force-were identified using in-situ dynamic measurements. Then, these experimental values were compared with the values calculated by empirical formulas suggested in Eurocode 8 to demonstrate that these formulas were applicable for the cases of rammed earth structures. Then, modeling was done to find a simple suitable model for rammed earth structures. Laboratory experiments were developed to measure the Poisson’s ratio which was necessary for the models. The results provided by the shear-beam model were close to that of in-situ experiments, which showed a shearing behavior of rammed earth structures. Elements which influenced the dynamic behavior of this structural type were also discussed. Understanding the dynamic characteristics of rammed earth structures will help engineers in their design of new rammed earth buildings but also in earthquake analyses of existing rammed earth buildings.     

Hygrothermal analysis of a stabilised rammed earth test building in the UK

This paper describes the analysis of the hygrothermal behaviours of stabilised rammed earth (SRE) walls used in a building in the UK. The analysis was achieved by computer simulation using WUFI Plus v1.2 whole building hygrothermal analysis software. To validate the model, an unoccupied test room in an unheated SRE building was monitored for 10 months. The hygrothermal properties of the SRE material were measured in the laboratory. It is shown that the SRE walls significantly reduced the amplitude of relative humidity fluctuations in the room air and reduced the frequency of high humidity periods at the wall surface. By adapting the model to represent an occupied and conditioned space, it is demonstrated that SRE walls have the potential to reduce the energy demand for humidification/dehumidification plant.     

Durability of rammed earth walls exposed for 20 years to natural weathering

This paper presents a study on the durability of different types of stabilised and unstabilised rammed earth walls. These rammed earth walls were constructed and exposed for 20 years to natural weathering, in a wet continental climate. None of these walls have shown complete collapse to date. A method to measure the rammed earth walls erosion by stereo-photogrammetry has been developed. The result shows that the mean erosion depth of the studied walls is about 2 mm (0.5% wall thickness) in the case of rammed earth wall stabilised with 5% by dry weight of hydraulic lime and about 6.4 mm (1.6% wall thickness) in the case of unstabilised rammed earth walls. The stabilisation enables to not use any plaster to protect the walls. In the case of the unstabilised rammed earth walls, an extrapolated lifetime longer than 60 years can be assessed. This shows a potential for the use of unstabilised rammed earth in the similar climatic conditions with this study. The method of stereo-photogrammetry used to measure the erosion of rammed earth walls on site may also help to calibrate and develop more pertinent laboratory test to assess the durability of rammed earth wall.     

Micromorphological description of vernacular cob process and comparison with rammed earth

Past builders have developed very low-embodied energy construction techniques optimizing the use of local building materials. These techniques are a source of inspiration for modern sustainable building. Unfortunately, this know-how was orally transmitted and was lost as earth construction fell into disuse during the 20th century in European countries. The absence of written documents makes necessary to use an archaeological approach in order to rediscover these construction strategies. Micromorphological analysis of thin sections collected in earth building walls was used for the first time to describe cob construction technique and highlighted several typical pedofeatures allowing to clearly identifying this process. Finally, a first comparison of the cob and rammed earth micromorphological features permitted to identify two key factors to distinguish these two techniques, the manufacturing state (solid or plastic) and the organization of the material in the wall.     

青海地区改性夯土材料抗压性能试验研究

为改善传统夯土墙的力学性能,使用青稞秸秆、石子、聚乙烯醇、固化剂、防水剂对夯土进行改性,通过对改性夯土试件进行无侧限抗压试验,分析改性试件的抗压强度、荷载-位移曲线.结果表明,添加青稞秸秆可以改善夯土试件脆性破坏的特性;夯土中掺入0.25％青稞秸秆、20％石子和0.8％固含量的聚乙烯醇时,改性试件的抗压强度比素土试件提...     

Energy use and thermal comfort in a rammed earth office building

A two-storey rammed earth building was built on the Thurgoona Campus of Charles Sturt University in Albury-Wodonga, Australia, in 1999. The building is novel both in the use of materials and equipment for heating and cooling. The climate at Wodonga can be characterised as hot and dry, so the challenge of providing comfortable working conditions with minimal energy consumption is considerable. This paper describes an evaluation of the building in terms of measured thermal comfort and energy use. Measurements, confirmed by a staff questionnaire, found the building was too hot in summer and too cold in winter. Comparison with another office building in the same location found that the rammed earth building used more energy for heating. The thermal performance of three offices in the rammed earth building was investigated further using simulation to predict office temperatures. Comparisons were made with measurements made over typical weeks in summer and winter. The validated model has been used to investigate key building parameters and strategies to improve the thermal comfort and reduce energy consumption in the building. Simulations showed that improvements could be made by design and control strategy changes.     

Experimental investigation on the compressive strength of cored and molded cement-stabilized rammed earth samples

This research aims to improve the insufficient and inadequate quality control techniques currently available on cement-stabilized rammed earth construction sites. To achieve this goal, the comparison between the compressive strength of cored and molded cylindrical samples have been experimentally investigated. In order to gain a deeper understanding of the additional causes influencing the strength of rammed earth samples, investigations on specimen slenderness, size, shape and capping methods have been also conducted. This study shows that in certain cases the mechanical behavior of concrete and cement-stabilized rammed earth are similar. The obtained results also indicate that the strength of cored specimens is always lower than that of molded specimens. A list of recommendations for the assessment of cement-stabilized rammed earth strength is proposed.     

Loading-unloading shear behavior of rammed earth upon varying clay content and relative humidity conditions

This paper investigates the impact of clay and moisture contents on the shear behavior of compacted earth taking into account loading-unloading cycles. Fine sand was added to a natural soil, thereby obtaining three different soils with clay contents of 35%, 26%, and 17%, respectively. A series of triaxial tests was conducted on samples previously equilibrated at three different values of relative humidity (RH). The evolution of failure strength f_c, Young's modulus E, and residual strain ε_res was investigated according to the clay content and the RH, the last two parameters being measured during the loading-unloading cycles. Firstly, the relative humidity at which the samples were fabricated and conditioned was seen to have a strong impact on the mechanical characteristics of the earthen material. An increase in RH led to a decrease in both failure strength f_c and Young’s modulus E, and an increase in plastic strain. The tendencies were found to depend on the clay content of the samples. Secondly, with an increasing stress level, a progressive decrease in Young’s modulus and an increase in residual strain ε_res (after a loading-unloading cycle) appeared. Thirdly, within the range of the investigated clay contents, both failure strength f_c and residual strain ε_res increased with an increasing clay content at constant values of RH and confining pressure, the rate of this increase being a function of the RH. Young’s modulus E was relatively insensitive to changes in the clay content, its variation being less than 20% for all cases. Finally, based on a particular definition of Bishop's effective stress, involving a specific functional form χ(s), the failure states of all the samples were observed to lie approximately on a unique failure line crossing the origin in the (p′-q) plane regardless of the matric suction and confining pressure.     

灾后重建中夯土墙民居现场抗震试验研究与实践

对西南山区使用较广泛的夯土墙进行了现场墙片抗剪性能试验与土样直接剪切试验,研究夯土墙体在单调荷载作用下的夯土墙承载力指标和破坏形态,并对夯土墙抗剪承载力的主要影响因素进行了探讨,提出夯土墙抗剪强度计算的建议公式。在试验研究的基础上,对当地典型夯土墙结构农房进行了抗震设计及施工工艺改良,并且指导建造了33户新型夯土墙农房,起到了很好的示范作用。     

基于SH加固材料的土遗址夯土试样室内滴渗试验研究

表面严重风化是中国西北干旱地区土遗址的主要病害之一。目前解决防风化问题的主要方法是通过研制的防风化加固材料进行工程加固和修复,然而防风化加固材料的研制尚无法满足实际工程的要求。系统研究了不同浓度SH滴渗夯土试样表面渗透半径和渗透速率的分布变化规律,及渗透加固后试样波速和崩解性的变化。试验结果表明,单孔最优注浆量为30~40 m L,此时滴渗时间约为300 min,最终表面渗透半径为3~4 cm。渗透后试样波速升高,抗崩解性能明显提高,以1.0%SH渗透后最为明显。