An overview of the remaining challenges of the RILEM TC 274-TCE, testing and characterisation of earth-based building materials and elements

Based on the RILEM Technical Committee 274-TCE work, this paper is a discussion of the remaining engineering challenges faced by earthen architecture. The assessment of earth material performances requires the development of appropriate procedures and standards. This is discussed in particular for the characterisation, hygrothermal behaviour, mechanical behaviour, and durability of earth materials. One other important challenge, since one of the main advantages classically put forward, is its ecological performance, is a proper assessment of life cycle assessment of earth materials, elements and buildings. Moreover, the paper develops why the approach to earthen construction must be different compared to the dominant construction materials, to preserve its ability to contribute to the ecological transition in the construction sector. In particular, the needs of using local soils, with an architectural approach coping with the limits of the materials, and developing an architectural optimisation to preserve the earthen materials multifunctionality rather than selecting a sole property to be maximised. Lastly, the findings of the paper can be used to develop a holistic approach to earthen construction to foster the development of new earthen architecture projects.

Reveal of Internal, Early-Load Interfacial Debonding on Cement Textile-Reinforced Sandwich Insulated Panels

Internal interfacial debonding (IID) phenomena on sandwich façade insulated panels are detected and tracked by acoustic emission (AE). The panels are made of a thin and lightweight cementitious composite skin. In the lab, the panels are tested under incremental bending simulating service loads (i.e., wind). Local (up to 150 mm wide) skin-core detachments are reported in the early loading stage (at 5% of ultimate load) and are extensively investigated in this study, since IID can detrimentally affect the long-term durability of the structural element. A sudden rise in the AE hits rate and a shift in the wave features (i.e., absolute energy, amplitude, rise time) trends indicate the debonding onset. AE source localization, validated by digital image correlation (DIC) principal strains and out-of-plane full-field displacement mapping, proves that early debonding occurs instantly and leads to the onset of cracks in the cementitious skin. At higher load levels, cracking is accompanied by local debonding phenomena, as proven by RA value increases and average frequency drops, a result that extends the state-of-the-art in the fracture assessment of concrete structures (Rilem Technical Committee 212-ACD). Point (LVDT) and full-field (AE/DIC) measurements highlight the need for a continuous and full-field monitoring methodology in order to pinpoint the debonded zones, with the DIC technique accurately reporting surface phenomena while AE offers in-volume damage tracking.

RILEM TC 247-DTA round robin test: sulfate resistance, alkali-silica reaction and freeze–thaw resistance of alkali-activated concretes

The RILEM technical committee TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ conducted a round robin testing programme to determine the validity of various durability testing methods, originally developed for Portland cement based-concretes, for the assessment of the durability of alkali-activated concretes. The outcomes of the round robin tests evaluating sulfate resistance, alkali-silica reaction (ASR) and freeze–thaw resistance are presented in this contribution. Five different alkali-activated concretes, based on ground granulated blast furnace slag, fly ash, or metakaolin were investigated. The extent of sulfate damage to concretes based on slag or fly ash seems to be limited when exposed to an Na2SO4 solution. The mixture based on metakaolin showed an excessive, very early expansion, followed by a dimensionally stable period, which cannot be explained at present. In the slag-based concretes, MgSO4 caused more expansion and visual damage than Na2SO4; however, the expansion limits defined in the respective standards were not exceeded. Both the ASTM C1293 and RILEM AAR-3.1 test methods for the determination of ASR expansion appear to give essentially reliable identification of expansion caused by highly reactive aggregates. Alkali-activated materials in combination with an unreactive or potentially expansive aggregate were in no case seen to cause larger expansions; only the aggregates of known very high reactivity were seen to be problematic. The results of freeze–thaw testing (with/without deicing salts) of alkali-activated concretes suggest an important influence of the curing conditions and experimental conditions on the test outcomes, which need to be understood before the tests can be reliably applied and interpreted.

Influence of Environmental Factors on the Swelling Capacities of Superabsorbent Polymers Used in Concrete

Superabsorbent polymers (SAP) are of major interest as materials to control the cement hydration process. The swelling behavior of the SAPs significantly influences the performance of the resulting concrete by slowly releasing polymer-bound water in order to maintain a consistent w/c value. A round-robin test conducted by the RILEM Technical Committee 260-RSC showed that the same batch of polymer can lead to large deviations in concrete performance and this was assumed to originate in different storage conditions of the SAP. In this contribution the change in the performance of two SAPs, a crosslinked poly(acrylate) and a crosslinked poly(acrylate-co-acrylamide), was assessed after ageing in standard climate, at 50 °C, and under UV irradiation. During storage in standard climate or 50 °C, ageing led to dehydration of the SAP, and this subsequently led to a higher water uptake during swelling. By contrast, UV irradiation reduced the water uptake, most likely as a result of photo-crosslinking. Dynamic water vapor sorption experiments indicated a strong dependence of the water uptake on both the ambient humidity and the temperature. As a result, cement mixtures containing SAP must be calculated on the dry mass of the SAP rather than the actual weight on site. A standard procedure of how to pack and handle SAP to be used in concrete is also provided.

Slurry surfacing: a review of definitions, descriptions and current practices

Cold bitumen emulsions (CBE) are currently used worldwide for both non-structural (cold surface treatments) and structural (cold bituminous mixtures) paving applications. Among non-structural applications, bituminous slurry surfacings (BSS) allow to improve surface properties and extend the pavement’s life. However, selection of constituents, mix design, application and quality control procedures for BSS are mostly based on local experience and empirical tests. Thus, the use of BSS is associated to higher technical risks with respect to the use of traditional hot-mix technologies. In this context the RILEM Technical Committee 280-CBE TG2 “Multiphase characterisation of cold bitumen emulsion materials” aims to collect worldwide theoretical knowledge and experiences on BSS and to inspire new standards, specifications and guidelines encompassing the wide set of existing practices. This paper summarizes the first part of the literature review carried out as part of the TC workplan and focuses on the definition, the description and the application method for BSS. National standards, construction specifications and best practice documents from North America, South America, Europe and Australia are analysed and compared.

Numerical Modelling of the Experimental Response of SRG Systems

Modern repairing and retrofitting methods for existing structures make use of composite materials, consisting of high strength textiles and a matrix, which can be either polymeric or inorganic. These kinds of techniques have been largely applied to masonry structures, since they significantly improve structural performance with a small increase of weight and a minimum invasiveness. However, the application of organic gluing agents on masonry has revealed some well-known drawbacks, which are almost all overcome resorting to inorganic matrixes, namely cement or lime mortars. An entire class of composites is thus identified as TRM (Textile Reinforced Mortars) or FRCM (Fibre Reinforced Cementitious Matrices). Among them, Steel Reinforced Grout (SRG) are characterized by Ultra High Tensile Strength Steel (UHTSS) cords embedded in mortar matrix and their use to improve the structural performance of existing historical masonry buildings is becoming more and more diffused. Qualification tests and acceptance criteria for SRG have just been defined. Nonetheless, numerical simulation of current available test procedures is mandatory to identify peculiar aspects of the response that at a following stage become an integral part of large scale models, when entire reinforced structures or portions need to be analysed. To this end, this work presents the numerical modelling of two different direct tensile tests on SRG systems: the Clamping-grip setup (RILEM Technical Committee 232-TDT 2016) and the Clevis-grip setup (ICC-ES AC434 2016). Numerical models able to replicate experimental tests and catch fundamental differences in their failure mechanisms are present

Assessing the performance of earth building materials: a review of recent developments

After being almost abandoned at the end of the Second World War, the use of raw earth is currently regaining the interest of architects, engineers and policy makers for the construction of dwellings in industrialised countries. This renaissance is driven by growing ecological awareness and the promotion of construction techniques that minimize energy consumption and carbon emissions. Raw earth displays very interesting thermo-hygro-mechanical properties, which can contribute to the reduction of the environmental impact of buildings not only during construction but also during service life. Nevertheless, one of the reasons that still prevents dissemination of raw earth into construction practice is the lack of commonly agreed procedures for assessing material performance. The RILEM technical committee TCE 274 has been established as a first step for overcoming this obstacle. The objective of the technical committee is to critically examine current testing procedures in order to propose suitable experimental standards. The results of this work will be presented in future publications while the present paper summarizes the main challenges faced by the committee and briefly describes some of the existing procedures for measuring the engineering properties of earth materials.

Experiences from RILEM TC 235-CTC in recommending a test method for chloride threshold values in concrete

Chloride threshold value is an important input parameter in service life predictions. There has been a need for a reliable method for testing this value in order to improve the understanding of basic factors influencing the corrosion initiation. For this reason RILEM technical committee (TC) 235-CTC was formed with the ultimate aim to recommend a suitable test method capable of delivering data with acceptable measurement uncertainty. During the TC’s life, a test method was proposed and a Round-Robin Test (RRT) was organised to evaluate it. Due to the unexpected results from the RRT, the ultimate aim of the TC was not reached. There were some experiences obtained from the TC’s work especially in designing the test method which are worthy for supporting future researchers continuing to search for a reliable test method for it. This technical letter presents the TC’s experiences.