Matériaux et constructions

The objective of this research was to incorporate recycled aggregate into pervious concrete to create a very sustainable concrete product for many applications. The research methodology interested replacing natural aggregate with recycled aggregate in the pervious concrete production at 4 different replacement levels of 25, 50, 75 and 100 %, with two different water-to-cement ratios of 0.27 and 0.32. Single sized recycled and natural aggregate, passing from 12.5-mm sieve and retained on 9.5-mm sieve, were used in the manufacturing of pervious concrete. Totally ten different concrete mixtures were produced and each of the concrete batches was tested for dry density, porosity, compressive and splitting tensile strength, water permeability and abrasion resistance. The properties of pervious concrete produced with recycled aggregate were also evaluated by statistical technique, namely GLM-ANOVA. The experimental results showed that the properties of pervious concrete were significantly affected by using recycled aggregate. Substituting the natural aggregate with recycled aggregate resulted in a considerable increment in permeability coefficient. However, it was observed that the mechanical properties of such concretes were adversely influenced up to a certain degree.

Một phương pháp thử nghiệm để xác định độ bền và đặc tính gãy của liên kết của các thanh ghép dán trong các kết cấu gỗ được trình bày. Kết quả thử nghiệm từ một loạt các thử nghiệm sử dụng phương pháp đề xuất cũng được cung cấp. Phương pháp thử nghiệm này cho phép ghi lại phản ứng toàn bộ về ứng suất và biến dạng của các mẫu thử nhỏ. Phản ứng này bao gồm hành vi mềm mại sau ứng suất cực đại, tức là ứng suất giảm khi biến dạng tăng. Loạt thử nghiệm bao gồm ba loại keo, hai loại vật liệu thanh, bốn góc tải trọng so với thớ gỗ và hai chất lượng gỗ với mật độ khác nhau. Một phương pháp để đánh giá hành vi gãy-mềm mại cũng được đề xuất. Hành vi mềm mại của sự gãy được đánh giá chỉ bằng cách sử dụng một phần của đường cong ứng suất-biến dạng. Phần được sử dụng trong việc đánh giá được xác định dựa trên độ dốc của phần giảm của đường cong ứng suất-biến dạng.

The purpose of this paper is an investigation of the possible role of supplementary cementing materials (SCMs) on the water retaining ability of hydrated lime (CL90) and Portland cement (PC) mortars. Desorptivity (R) defines the water retaining ability of mortars in the freshly-mixed wet state. Transfer sorptivity (A) defines the ability of the substrate to withdraw water from the wet mix. The time to dewater (t dw), is an expression derived from the sharp front theory, and enables calculation of the time taken for a wet mortar joint to be dewatered by an absorbent substrate. The results show that the very water retaining CL90 mortars become progressively more water releasing with increased volume fraction replacement levels of both ground granulated blast-furnace slag (GGBS) and fly ash (FA). On the other hand, the very water releasing PC mortars become more water retaining with the addition of silica fume (SF). Results also show that transfer sorptivity increases as the volume fraction replacement levels of GGBS and FA increases in CL90 mortars and decreases with increased volume fraction replacement levels of SF in PC mortars. Since the time taken to dewater a mortar joint (t dw) is inversely proportional to the squared transfer sorptivity, t dw can be dramatically altered by the addition of SCMs in both CL90 and PC mortars. These parameters have important practical consequences, not only in the initial adhesion of the mortar to the substrate but also in the strength of the set material. The ability to manipulate the water retaining properties can also allow construction time to be reduced.

To respond to the rapid introduction and development of calcined clays as supplementary cementitious material (SCM), the toolbox of characterization methods for cementitious materials requires extension to raw clay characterization. Borrowing concepts and methods developed in the field of clay mineralogy, this paper outlines the merits and limits of widely accessible characterization techniques for raw clays intended for use as SCM, when calcined. The paper focuses mainly on the identification and quantification of the raw clay mineral components, as these characteristics have important implications for further material processing and performance. General notes are provided on clay sampling and pre-treatment as well as bulk chemical analysis. The main techniques considered are X-ray diffraction, thermal analysis and infrared spectroscopy. Their application on raw clays is introduced, highlighting clay-specific aspects of sample preparation, data acquisition, and processing. Guidelines and interpretation tables are provided to aid in the analysis of the acquired data, while limitations and potential interferences are identified. Options for remote prospection by infrared spectroscopy are included as well. To illustrate the type of information to be gained and the complementarity of the techniques, two representative raw clays are fully characterised. This paper aims to highlight that mineralogical characterization is a feasible and often necessary step in the study and assessment of raw clays that can deliver a wealth of informative data if carried out appropriately.

This study investigates the combined effect of the strain rate and temperature on the compressive properties of hybrid fiber ultra high toughness cementitious composites (UHTCCs) using a Split Hopkinson pressure bar. Specimens were first heated to different exposure temperatures, e.g. ambient temperature, 200, 400, 500, 600 and 800 °C, and subsequently, cooled to ambient temperature. Thereafter, the specimens were tested at four different strain rates. The test results show that the dynamic compressive strength of the UHTCC is enhanced at a temperature of 200 °C, and subsequently, decreases with the increase in exposure temperature. The strain rate sensitivity of UHTCC is largely enhanced with the increase in exposure temperature. The possible mechanism of this phenomenon was discussed based on the high-speed photography of the crack propagation process on the surface of the specimens and microscopic observation of fibers condition on their fracture surfaces. Moreover, an empirical relationship is established to express the dynamic strength enhancement of fire-damaged UHTCC as a function of strain rate.

The model for drying creep from Part III is here extended for the temperature effect. The basic, additive form of the double power law and the shrinkage-like term are preserved, but certain coefficients become temperature-dependent to reflect the acceleration of drying and of aging. Satisfactory agreement with test data is achieved.

Anaerobic digestion allows renewable energy to be produced through the degradation of bio-waste. The process, which is of economic and ecological interest, is implemented industrially in concrete digesters. Bio-waste is a complex medium with a composition that can vary in time and space. It contains several chemical compounds, including volatile fatty acids, ammonium, and CO2, which are aggressive towards concrete and compromise its durability. The individual effects of the different compounds on concrete are significantly different. To move toward a better design of concrete intended for the building of biogas digesters, this paper aims to understand the mechanisms and intensity of alteration associated with the different components of biowaste and their contribution to the total deterioration. Ordinary Portland cement pastes were immersed for 16 weeks in six synthetic solutions made of the three metabolites, taken alone or in mixes. The mass variations of the specimens, the pH, and the concentration of the chemical elements in solution were monitored over time. The microstructural, chemical and mineralogical changes of the samples were analysed by scanning electron microscopy, electron probe micro-analysis and X-Ray diffraction analyses and showed phenomena of dissolution, leaching and carbonation. The results show that the acetic acid solution was the most aggressive, in accordance with its pH value, and had a predominant effect in mixed solutions, whereas sodium bicarbonate solution induced carbonation and showed a protective effect. Interestingly, despite its reputed high aggressiveness, ammonium nitrate did not have a major impact in mixed solutions.

This article presents finite element modelling to predict the early age cracking risk of concrete structures. It is a tool to help practitioners choose materials and construction techniques to reduce the risk of cracking. The proposed model uses original hydration modelling (allowing composed binder to be modelled and hydric consumption to be controlled) followed by a non-linear mechanical model of concrete at early ages involving creep and damage coupling. The article considers hydration effects on this mechanical model, which is based on a non-linear viscoelastic formulation combined with an anisotropic, regularized damage model. Details of the numerical implementation are given in the article and the model is applied successively to a laboratory structure and to a massive structure in situ (experimental wall of a nuclear power plant studied in the framework of the French national research project CEOS.fr).

Due to the particularity of highway tunnel structure, traffic accidents are easy to cause severe fires on bituminous pavement. Fire leads to the thermal decomposition of bituminous pavement, resulting in very serious consequences. In this study, such flame retardants as expanded graphite, ferric hypophosphite, ammonium polyphosphate and zinc borate were mixed at a mixing ratio of 1:3:4 to prepare composite flame retardant (CFR). Flame-retarding warm mix agent (FWA) was developed by loading CFR on porous warm mix agent (WMA). The thermal decomposition properties of WMA, FWA and CFR were studied using differential scanning calorimetry/ thermogravimetry. Then, suppression effects of CFR and FWA on thermal decomposition and combustion kinetics of bitumen were investigated. Influences of CFR and FWA on morphology and composition of bituminous combustion residues were studied using field emission-scanning electron microscopy. Test results show that flame retardant constituents in CFR decompose in turn during the continuous temperature rise, which effectively inhibits whole process of bituminous thermal decomposition and combustion. WMA shows a collaborative promotion action on CFR, and effectively improves the dispersion of CFR in bitumen. Moreover, WMA promotes the formation of denser and thicker carbonized layers. FWA significantly inhibits thermal decomposition behaviors of bitumen and adsorbs many macromolecular volatiles.

The performance of various composite materials applied to strengthen hollow masonry panels under out-of-plane actions is compared here. The strengthening solutions belong to three reinforcement Externally Bonded (EB) wet lay-up systems: (i) bidirectional composite meshes applied with inorganic matrices, i.e., Textile Reinforced Mortars (TRM); unidirectional composite textiles applied with (ii) inorganic matrices, i.e., Steel Reinforced Grouts (SRG), or (iii) organic (epoxy) matrices, i.e., Fibre Reinforced Polymers (FRP), Steel Reinforced Polymers (SRP) and Natural FRPs. Carbon FRP, flax and hemp NFRP, and basalt and glass-based TRM were examined. As inorganic matrix, a cement-based mortar was used for TRMs; in the case of SRGs, comparisons with a magnesia-based matrix were also carried out. Twenty-seven specimens were subjected to simplified four-point monotonic bending tests, aimed at reproducing in the laboratory the failure condition of infill masonry walls under out-of-plane actions. The results are compared in terms of failure mode and mechanical improvement, and provide an analytical evaluation of moment–curvature behaviour according to bilinear laws.