Hydro-Mechanics Coupling on Rammed Earth Material: Drying Experiment at Structural Scale

Rammed earth structures are very sensitive to hydric conditions. Experimental studies have been undertaken to understand the link between liquid water transfer and mechanical behavior at structural scale. This study was done on a prismatic rammed earth sample of 15cm x 15cm x 45cm, structured as a wall element with several layers. Samples were subjected to one dimensional drying in an indoor environment. Humidity and temperature sensors were placed on each layer inside the sample. The kinetic of drying was monitored by continuous weighing the sample and humidity measurement at a regular interval. Results of water content evolution suggest that samples dry in two stages; the first stage is associated with relatively high evaporation flux of 13.88 g m-2h-1 while the second stage has very low flux of moisture evaporation. Unconfined compressive strength was performed in drying samples after 0, 2, 6 and 8 weeks of drying. In parallel, digital image correlation was used to determine the stiffness of samples. Results show an increase in compressive strength by the rate of 98 kPa per week in the first two weeks, then this rate reduces to 23 KPa per weeks after 8 weeks. These experimental results will allow to enhance the 3D hydro mechanical numerical model developed in the laboratory.

Variability Assessment of the Compressive and Tensile Strength of Fibred Earthen Composites

Earthen composites (rammed earth, cob, adobe, daub, CEB...) are experiencing renewed interest from builders due to the many advantages of these building materials, and in particular their eco-friendliness. Nevertheless, the widespreading of these materials, as certified materials and conforming to construction standards, comes against the lack of data concerning their mechanical properties. Indeed, the literature generally gives the average values of the properties without indicating the number of specimens tested neither the distribution of the data. Yet, the mean value of the compressive strength is not enough to assess the reliability of a given earthen composite to build a wall and it would be better to indicate the value of a defined percentile (characteristic value just like with concrete composites). The aim of this paper is to analyze the data about the mechanical properties (tensile and compressive strength) obtained on different formulations of cob including natural fibres or not. The tests performed allowed to determine the probability density function and the average values, the standard deviation and the percentiles, for the various properties.

Mortar to Repair Rammed-Earth Walls’ Surfaces: Do we still Need it?

A rammed-earth technique has been echoed worldwide due to being conceived not only as an environment-friendly method of construction but also standing as an alternative method to arguably replacing cement. The technique however shows several pitfalls. One concerns the lengthy process of curing upon erecting the rammed-earth walls due to the low process of a chemical reaction occurred throughout the curing stage. A second bias followed from the slow curing and concerns the degradation accentuated at the outer wall’s texture, particularly at the edges, due to effects of the weather cycle. These drawbacks have been observed while accomplishing a funded research project. This article has at its stake remedying the above pitfalls. A natural sandy limestone shows a low percentage of calcium carbonate needed for a cohesive mixture. The method suggested here is based on an experiment that uses minerals of the fruits’ and vegetables’ waste as a binding substance. Curing time in this method has been reduced to the half. It is also suggested here that each stage has its importance, including mixing the soil particles dry and wet, compacting the moistened soil mixture, a well-made formwork and curing, towards remedying the above pitfalls.

Mechanical Properties of Rammed Earth Stabilized with Local Waste and Recycled Materials

Traditional techniques of construction using natural and locally available materials are nowadays raising the interest of architects and engineers. Clayey soil is widely present in all continents and regions, and where available it is obtained directly from the excavation of foundations, avoiding transportation costs and emissions due to the production of the binder. Moreover, raw earth is recyclable and reusable after the demolition, thanks to the absence of the firing process. The rammed earth technique is based on earth compressed into vertical formworks layer by layer to create a wall. This material owes its strength to the compaction effort and due to its manufacture procedure exhibits layers resembling the geological strata and possessing high architectural value. The hygroscopic properties of rammed earth allow natural control of the indoor humidity, keeping it in the optimal range for human health. Stabilization with lime or cement is the most common procedure to enhance the mechanical and weather resistance at once. This practice compromises the recyclability of the earth and reduces the hygroscopic properties of the material. The use of different natural stabilizers, fibers, and natural polymers by-products of the agriculture and food industry, can offer an alternative that fits the circular economy requirements. The present study analyses the mechanical strength of an Italian earth stabilized with different local waste and recycled materials that do not impair the final recyclability of the rammed earth.

Benefit of Unsaturated Soil Mechanics Approach on the Modeling of Early-Age Behavior of Rammed Earth Building

Rammed earth has the potential to reduce the carbon footprint and limit the energy consumption in the building sector due to its sustainable characteristics. Still, its use is not generalized due to a lack of understanding of the material behavior, notably its sensitivity to water. The coupled hydro-mechanical behavior has been recently studied in the framework of unsaturated soil mechanics, using suction as the parameter to represent the hydric state. This dependency of the mechanical behavior on the hydric state leads to uncertainty of the drying period required to progress in the construction process. Notably, the drying period before building the next floor is unknown. To determine the drying period, thermo-hydro-mechanical coupled finite element method simulations were carried out on a single wall by using the unsaturated soil mechanics approach and safety criterion recommendations from the practical guide for rammed earth construction in France. It was determined that it takes significant time for the construction of additional floor both in ‘summer-like’ and ‘winter-like’ environmental conditions, whereas the walls were far away from the ultimate failure state. Thus the drying periods were overestimated. It was concluded that the safety criterion from the practical guide is very conservative and drying periods can be reduced without significantly compromising the safety factor.