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%.     

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.     

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.     

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.     

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.     

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.     

Seismic resistance of earth construction in Portugal

This paper presents an assessment of the potential seismic performance of new earth construction in Portugal. Results of a parametric study on a properly designed rammed earth construction, considering several strengthening solutions, are presented and discussed. It is concluded that single storey houses can have acceptable seismic performance even in high seismicity areas, provided that the structure is adequately strengthened by reinforced concrete columns and beams. Improvement of the characteristics of the structural material (earth) may be necessary to reduce damage.     

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。     

Durability evaluation of building sealants by accelerated weathering and thermal analysis

Accelerated weathering tests, exposure to heat (80 °C) and UVA ultraviolet radiation (300 W), were carried out respectively on two selected building sealants, silicone and polyurethane, in this paper. A quantificational term, deviation coefficient, was proposed to rationally evaluate the sensitivity of sealants to the different weathering conditions and sealants’ durability. The study has shown that the weathering period should be at least 5000 h in order to let distinct change on sealants’ property occur. The study has also proved that different weathering conditions have completely different influences on the properties and structures of sealants, and thermogravimetry and differential scanning calorimetry could verify their ageing mechanisms.     

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。     

Assessing the moisture-content-dependent parameters of stabilised earth materials using the cyclic-response admittance method

The cyclic-response admittance method is discussed along with its suitability for assessing the moisture-content-dependent thermal properties of porous fabrics under idealised dynamic conditions. The effects of insulation positioning in composite stabilised earth wall fabrics are analysed. The moisture dependent non-steady-state parameters of Y, f, ? and ω are presented for a range of stabilised earth materials in relation to their degree of saturation, S_r. Data to allow direct comparisons between specific cross-sectional composite wall fabrics using both conventional materials and stabilised earths are given. The effects of moisture-content distribution within stabilised earth wall fabrics is analysed in terms of the overall effect on the wall's non-steady-state parameters. The cyclic-response admittance method is modified to incorporate the moisture dependent non-steady-state parameters and the effects on admittance, decrement and time lag are discussed.     

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...     

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.     

预应力返包式加筋土挡墙的动力响应分析

在地震作用下,返包式加筋土挡墙作为一种柔性结构常因侧向变形较大或局部产生破坏而影响其正常使用。为解决该问题,提出了预应力返包式加筋土挡墙结构。为完善预应力返包式加筋土挡墙的设计理论,运用拟动力法和附加应力法理论,以预应力返包式加筋土挡墙作为研究对象,结合现有的加筋土挡墙侧向动土压力和侧向位移计算理论,提出了一套用于计算预应力返包式加筋土挡墙侧向动土压力和侧向位移的理论公式。结合室内振动台模型试验验证了所提理论方法的可行性和合理性。该方法计算简洁,适用性广,能够较好地计算预应力返包式加筋土挡墙的侧向动土压力和侧向位移,对完善预应力返包式加筋土挡墙的设计理论具有一定的指导和借鉴意义。     

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...     

挡土墙被动土压力的滑移线解

基于极限平衡理论,视墙后填土为服从Mohr-Coulomb屈服准则的理想弹塑性材料,并且假定它是各向同性的、均匀的以及不可压缩（膨胀）的理想连续介质。引进了应力奇点及其应力边界条件,建立了静定可解的极限平衡边值问题数学模型,而不必考虑土的应力–应变关系,采用滑移线法求解了墙后塑性区的滑移线场和应力场,进而求解了挡土墙被动土压力和滑裂面土反力。通过无量纲分析,提出了几何力学相似原理。数值分析表明,被动土压力的滑移线解一般总是小于或等于库仑解,经典朗肯土压力或满足非奇异条件的经典库仑土压力与滑移线解一致,Hencky第一定理和第二定理不具有普遍适用性。     

计算柔性支挡结构主动土压力的简化方法

对于柔性支护挡土墙,在计算土压力时,宜考虑土压力作用点位置对其计算数值的影响。提出一个建立在Bishop法基础上的简化法。当土压力作用点位置为下三分点时,计算成果可无一例外地收敛到经典的库仑理论值。作用点位置为墙高中点时,经算例分析,主动土压力相应下三分点时的数值增加了15%左右。