Improved Thermal Transmittance Measurement with HFM Technique on Building Envelopes in the Mediterranean Area

Abstract Although the designed theoretical value of U can be derived from the thermal parameters of layers composing an opaque element, according to ISO 6946:2007, measurements are necessary to confirm the expected behaviour. Currently, the measurements of thermal transmittance based on Heat Flow Meter method (HFM) and according to standard ISO 9869-1:2014 are widely accepted. Anyway, some issues related to difficulties in measurements are present: the roughness of wall surfaces, the proper contact between the heat flow plate and the temperature probes with wall surfaces, undesired changes in weather conditions. This work presents the results obtained in thermal transmittance measurements with a modified HFM method, widely described in this paper. Differences between U-values obtained with the modified HFM method and theoretical ones were in the range 0.6 - 6.5 %. Moreover, the modified HFM method provided a result closer to the theoretical one, when compared to that obtained with standard HFM method (discrepancy with theoretical value were 0.6% and 16.4%, respectively)

Influence of Carding and Pressing on Hygrothermal Properties and Fire Reaction of Hemp Fiber Nonwoven Mats

This article depicts the effect of carding and pressing on hygrothermal properties of hemp fibers nonwoven mats, trying to understand if their implementation can improve their behavior when employed as insulation materials in buildings. Hemp fibers belonging to Cannabis Sativa species and coming from local area (Apulia - Italy) were examined, then samples of carded and pressed hemp fibers nonwoven mats were prepared. According to European standards, the thermal conductivity, the vapor permeability and the fire reaction of hemp fibers samples were measured. Results were compared to each other and with those of a commercial nonwoven mat made with hemp (90 wt. %) and synthetic fibers (10 wt. %), used as reference. We observed that carded and pressed hemp fibers were characterized by a lower thermal conductivity when compared to unprocessed hemp fibers, likely because the removing of wood elements. On the other hand, not processed hemp fibers show higher breathability when compared to carded and pressed ones, as well as with respect to the commercial nonwoven mat. Moreover, it was proved that the absence of synthetic commingled fibers in hemp fibers allows a better behavior in fire reaction. At last, the improvement in terms of insulation properties of a hollow brick when filled with hemp fibers was verified, by comparing the thermal conductivities of an empty and a filled hollow brick; as expected, the filled hollow brick shows a lower thermal conductivity, underlining the effectiveness of hemp fibers as insulation material

Hempcrete Buildings: Environmental Sustainability and Durability of Two Case-Studies in North and South Italy

In the framework of Circular Economy policies aimed at reducing the consumption of raw materials, shives, as an agricultural by-product of hemp cultivation, have gained a renovated life in the construction sector. Its excellent thermal insulating properties permitted the development of new building materials to be used in various executive technologies. When shives are mixed with a mineral binder such as lime or cement, the mixture is usually referred to as hempcrete. In Italy, the use of hempcrete and the development of new production chains and implementation techniques dates back only to about the last decade, while other European countries have more long-lasting experiences (90s). In order to assess the potential benefits of hempcrete in the construction sector, its environmental performances were evaluated using the LCA methodology, by comparing four non-loadbearing representative walls, one made with hempcrete blocks and the others with more “traditional” materials. This research constitutes a solid basis for the development of future guidelines and/or regulations at national and international level in order to guarantee the maximum diffusion of this type of product. Then, a study has been carried out regarding the functionality of hempcrete blocks in masonry, layered with finishing plaster made of fine hemp shives, to evaluate the in-situ hygrothermal building performance. In particular, measurement methods were developed and analysis were carried out on two houses, one in northern Italy and one in southern Italy, and precisely in Sicily, focusing the study on the performances of the walls subjected to warm Mediterranean climates. Indeed, the literature on masonry behavior in hot Mediterranean climates is much scarcer than in cold climates

Analysis of CFRP Joints by Means of T-Pull Mechanical Test and Ultrasonic Defects Detection

Defects detection within a composite component, with the aim of understanding and predicting its mechanical behavior, is of great importance in the aeronautical field because the irregularities of the composite material could compromise functionality. The aim of this paper is to detect defects by means of non-destructive testing (NDT) on T-pull samples made by carbon fiber reinforced polymers (CFRP) and to evaluate their effect on the mechanical response of the material. Samples, obtained from an industrial stringer having an inclined web and realized with a polymeric filler between cap and web, were subjected to ultrasonic monitoring and then to T-pull mechanical tests. All samples were tested with the same load mode and the same test configuration. An experimental set-up consisting of a semiautomatic C-scan ultrasonic mapping system with a phased array probe was designed and developed, optimizing control parameters and implementing image processing software. The present work is carried out on real composites parts that are characterized by having their intrinsic defectiveness, as opposed to the previous similar results in the literature mainly obtained on composite parts with artificially produced defects. In fact, although samples under study were realized free from defects, ultrasonic mapping found defectiveness inside the material. Moreover, the ultrasonic inspection could be useful in detecting both the location and size of defects. Experimental data were critically analyzed and qualitatively correlated with results of T-pull mechanical tests in order to better understand and explain mechanical behavior in terms of fracture mode

Combining the bi-objective approach and conditional coring for a reliable estimation of on-site concrete strength variability

In real practice, to assess concrete strength in structures, engineers usually use non-destructive tests (NDT) (e.g. rebound hammer or ultrasonic pulse velocity) in addition to destructive tests (DT) that are carried out on cores extracted from the structure. The results of these tests (NDT and DT) are used to identify a relationship (a conversion model) between the non-destructive measured features and the concrete strength. This model can be then used to assess the strength at any location within the structure under consideration, as well as the mean strength and the strength standard deviation (strength variability). In fact, the assessment of concrete strength variability is as important as the mean strength since the mean strength alone cannot provide a clear picture about the concrete under investigation. However, due to the presence of many uncertainties, the reliability of the values estimated by NDTs need to be improved. In the present study, a wide range of concretes having mean strengths of 10–50 MPa and concrete strength variabilities of 10–30% (defined by the coefficient of variation) is analysed. The main target of this paper is to analyse how would the reliability of assessing the concrete strength variability changes if the bi-objective method is used as a model identification approach and the conditional coring concept is applied for selecting core locations. Results are analysed in terms of the minimum number of cores NC that corresponds to a specific uncertainty level, concrete characteristics, and quality of NDT measurements. The results show an important improvement in the reliability of assessing the strength variability when both the bi-objective method and conditional coring are applied togethe

How to Identify the Recommended Number of Cores?

The concrete strength assessment process is influenced by uncertainties at many levels, including random measurement errors, sampling uncertainty and identification of the conversion model parameters. Therefore, instead of estimating the true value of the concrete strength, it is preferable to say that the objective of the assessment process is to predict a strength value ranging at a tolerable distance from the true strength value. This implies a deep revision of the assessment paradigm, in which both the acceptable tolerance interval and the risk of a wrong assessment must be given at the very beginning of the investigation. A large series of simulations has been carried out in order to understand and quantify how, for a given tolerance on the strength estimation, the risk value varies as a function of the precision of measurements, the number of cores and the strength distribution. Empirical models have been identified from the simulation results. These models have been finally used to calculate how many cores are required in various situations, to achieve the accuracy corresponding to three different estimation quality levels. This chapter describes the principles of the simulation, and how their results were used in order to build a series of tables where the recommended number of cores is made available in a variety of situations

Identification of Test Regions and Choice of Conversion Models

The main objective of test region (TR) identification is to define an efficient conversion model. The first part of the chapter aims a difficult question, the identification of test regions (TR) because each structure is specific and so it is impossible to give a unique methodology. Here, three different possibilities are proposed. The first one is based on synthetic data obtained on a continuous structure for which TR are identified by means of k-means clustering method. The second approach concerns a real building for which TR are determined by means of two different statistical methods based on the analysis of confidence interval and ANOVA. On three real case studies, the second part of the chapter compares the performances of two scenarios, either the consideration of several TRs and so a conversion model on each one, or the consideration of a unique TR with only one model. The efficiency of each scenario is quantified by the error on the estimation of both mean strength and local strength

Recommendation of RILEM TC249-ISC on non destructive in situ strength assessment of concrete

International audienceThis recommendation is written to improve the assessment of the in situ. Compressive strength of concrete in existing structures by combining core strength values and non-destructive measurements. Both average strength and its scatter are considered. Deriving a characteristic strength from the assessment results is not considered here. The recommendation applies for most common techniques (ultrasonic pulse velocity, rebound hammer, pull-out) but also for less common techniques (penetration test, etc.). The recommendation does not apply to situations in which no core has been taken from the existing structure and is limited to situations where NDT is combined with cores. The recommendation introduces the concept of Estimation Quality Level, corresponding to the target of assessment, and which is put in relation with the means and strategy developed for assessing concrete. The text details all steps that must be followed from the data gathering to the checking of the quality of the final estimations. For more clarity, an illustrative example is described for each step of the assessment process

How Investigators Can Assess Concrete Strength with On-site Non-destructive Tests and Lessons to Draw from a Benchmark

A benchmark is carried out in order to compare how 13 experts define and can carry out an NDT investigation program and derive strength values from NDT measurements. The benchmark is based on simulations, which reproduces a synthetic data set corresponding to a grid of twenty 3m-high columns defining the structure of a building made up of beams and columns. The experts must assess the mean and the standard deviation of compressive strength. Three levels of assessment are considered corresponding to different quantities of test results (destructive or non destructive) available for the experts. The comparison of the various strategies used by the experts and the analysis of results enables the identification of the most influential parameters that define an investigation approach and influence its efficiency and accuracy. A special emphasis is placed on the magnitude of the measurement error. A model of the investigation strategy is also proposed