Impedance spectroscopy was applied to Portland cement and its carbon nanotubes (CNT) composites to measure and describe the electrical conductance phenomena and their dependency on the moisture. Two series of composites were prepared, one with multi-walled, and the other with single-walled CNTs. The percolation concentration was reached only with the single-walled CNTs between 0.10 and 0.25 wt%; it was therefore possible to compare a percolative and a non-percolative system. The kinetic of the drying process was measured in the range of 24 h and described by a decay model with a stretched exponential to be correlated with the composite composition. The polarization phenomena occurring in the materials before and after the moisture removal were modelled with logistic sigmoid and explained by the morphology. In particular, the three found sigmoid were correlated to the polarization phenomena occurring at well-defined structural levels of the specimens. Their mathematical definition was shown to be fundamental for a correct interpretation of the Cole-plots of the real conductivity. Such phenomena presented a peak of intensity at a well define frequency but their effects spread across a broad range of Hertz. Moreover, over the AC frequency of 10 Hz, the conductive effect of the moisture overlapped the conductivity increase caused by the percolative network of the CNT. A dry sample is therefore necessary for accurately evaluating the source of the conductivity, a distinction which is crucially important for sensing applications.

A review of the mechanical property development of concrete containing calcined clay was performed. A comparison of compressive and tensile strength results showed that concrete can be made to have equivalent or higher strength as an ordinary portland cement (OPC) system with up to 30% calcined clay or 50% blend of calcined clay and limestone fines in a limestone calcined clay cement (LC3) system, as long as the kaolinite content in the clay used is above 40%. Most of the strength development in these systems occurs during the first 7 days, making extended wet curing not necessary in these systems. Calcined clay systems are subject to the cross-over effect because of the high solubility of ettringite and lower cement degree of hydration at elevated temperatures. Concrete creep and shrinkage were found to be a function of the clay kaolinite content and replacement level. Bond strength was improved by the use of up to 20% metakaolin.

This study investigates the potential use of basalt powder as a sole precursor or blended in high amounts in slag-based alkali-activated systems. Eight alkali-activated mixes are prepared and comprehensively analyzed to determine the compressive strength development and microstructural characterization of basalt powder-based and basalt powder/slag blends activated by sodium hydroxide and a mixture of sodium hydroxide and sodium silicate. The mixes are characterized from a microstructural viewpoint via X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric and scanning electron microscopy analyses. The results show that while basalt powder-based mixes have low compressive strength values, ranging between 2 and 9 MPa, basalt powder/slag blend mixes exhibit a moderate compressive strength, i.e., 20 MPa at 28 days. Furthermore, sodium-silicate-activated basalt powder/slag blend mixes achieve high compressive strengths at early and further ages. The low strength values of the basalt powder-based mixes are attributed to the low concentration of reactive species and lack of Ca2+ ions in the medium, while the high compressive strength of the blended mixes is mainly associated with the formation of calcium aluminosilicate hydrate [C–(A)–S–H] or Na-enriched calcium sodium aluminosilicate hydrate [C–(N)–A–S–H] gel phases along with the calcic-plagioclase, which afford a denser microstructure. The obtained results show that basalt powder can be used in high concentrations, i.e., 50%, in alkali-activated systems, and basalt powder/slag blends can be a feasible, alternative binder system for use as a structural material.

This study proposed an alternative method to define and measure the water absorption and specific gravity of aggregates. The classical Archimedes principle for measuring the density of objects was modified. Cement pastes and mortars were prepared using alcohol and water to measure the volume of the aggregate following centrifugal compaction (CC). Consequently, the volume of the paste and mortar after CC was evaluated using the mass of bleed liquid. Various experimental factors related to the CC method were considered, including the type of cement, type of solvent, revolution time, amount of initial liquid-to-cement ratio, and type of aggregate. The results obtained from CC with water and alcohol mixtures were verified using standard test methods. Thus, the water absorption and specific gravity of the aggregates under surface-saturated dry (SSD) conditions were confirmed to be measured using CC machine, regardless of the particle shape and pore structures of the aggregates.

To investigate the effects of different aggregate mixing schemes on the mechanical properties of concrete, this study proposes a method that can rapidly build a two-dimensional random aggregate model of mixed aggregate concrete. First, a deformed ellipse is used to represent the pebbles, and a method that can generate a model of the crushed stone with sharp edges is proposed. Second, a point cloud with state functions is constructed in the specimen space to improve the efficiency of aggregate placement. Third, the action scope and mathematical methods are combined to enable fast intrusion judgments between aggregates. Fourth, the aggregates are graded and classified according to the proportion of different types of aggregates in each level, which is controlled using the critical domain. Finally, simulations of crack propagation are performed on the specimens generated using three different aggregate mixing schemes. The simulation results show that the shape of the concrete aggregates and the proportion of different types of aggregates affect their mechanical properties, which is consistent with the findings of previous studies. The effectiveness of the modeling approach is verified by comparing the modeling efficiency analysis and simulation results.

Using split Hopkinson pressure bar (SHPB) to carry out the Brazilian disk test, for the calculation of the splitting tensile strain rate of the specimen, the method in the existing literature only considers the influence of the tensile stress, while in the actual splitting tensile process, the combined effect of compressive stress and tensile stress leads to a large error between the calculated strain rate and the measured strain rate. Therefore, the calculation of splitting tensile strain rate by the existing method is not accurate. To solve this problem, a new analytical method considering the tension–compression coupling was proposed in this study. The true strain rate of specimens can be obtained using the classical three-wave method of SHPB test and the basic performance parameters of bars and specimens. The results of this method were verified by numerical calculation and experiment. The results show that the strain–time history curve calculated by this method is highly consistent with the numerical results in terms of numerical verification, and the error range of strain rate is 1.2–8.6%. However, the error range of strain rate obtained using the existing method is 34.4–41.2%. The rising stage of strain–time history curve calculated by this method is highly consistent with the experimental results in terms of experimental verification, and the error range of strain rate is 1.7–14.7%. While the error range of strain rate obtained using the existing method is 47.2–58.5%. The existing method of splitting tensile strain rate will overestimate the dynamic tensile strength of material and make engineering design in a dangerous state.

The lower bond strength of FRP bars to concrete compared to steel bars has remained an unsolved barrier to the widespread use of FRP-reinforced concrete under extreme loading. Additionally, the degradation of the bond between FRP reinforcement and concretes in aggressive environments adds to the existing concern. In this study, an innovative anchorage system comprised of polypropylene pipe was used to strengthen the bond between seawater concrete and GFRP bars after 250 days of exposure to offshore environmental conditions. As material factors, two types of GFRP bars (sand-coated and ribbed) and two types of concrete (normal and seawater concrete) were evaluated. Four distinct environmental conditions were used to assess the samples: (i) ambient environment (control), (ii) tap water, (iii) seawater, and (iv) wet-dry cycles in seawater. According to the findings of the direct pull-out tests, the suggested anchor system strengthens the bond and shifts the failure mode from bond failure to bar rupture. Additionally, after exposure to 250 days of seawater wet-dry cycles, GFRP-reinforced seawater concrete lost 5% of its maximum bond strength (developed bar tensile stress). All other samples exposed to different environmental conditions either increased or decreased in bond strength by less than 5% after 250 days, compared to the control samples.

Innovative composite shear walls (ICSW) with multi-partition steel tubes and concrete have been increasingly used for improving seismic performance in engineering structures. However, limited research has focused on the interface bond behavior between steel tubes and concrete. This study aimed to investigate experimentally the bond performance through seven ICSW specimens subjected to push-out tests. The influences of the effective width-to-thickness ratio and adjacent cavity restriction conditions on the bond strength are discussed. It was found that the bond strength increased with a decrease in the effective width-to-thickness ratio of the steel tubes, and the adjacent cavity restriction condition had a slight influence on the bond strength. To determine peak bond strength, the simplified calculation formulas that considered the influence of the effective width-to-thickness ratio were developed. A theoretical bond-slip model for predicting the bond-slip behavior of multi-partition steel tubes and concrete was proposed, which was verified to be acceptable by comparison with the test results. The present study could provide the valuable data for engineering applications of ICSW structures.

Recent developments in understanding the rheology of mortar and concrete as well as applying this understanding in the practice of construction necessitate an accurate assessment of materials’ rheological properties. It is well known that different rheometers for mortar and concrete deliver different results, as this was shown over 15 years ago in two measuring campaigns comparing concrete rheometers. Considering newly developed rheometers, including those to evaluate interface rheology and structural build-up at rest, as well as additional measurement procedures and data interpretation techniques, a new comparison campaign was carried out in 2018 at the Université d’Artois, in Bethune, France. This new campaign focused on measuring workability characteristics, flow curves, static yield stress values, interface properties and tribological data. A total of 14 different devices capable of measuring one or more of the above-mentioned characteristics were employed. These devices included four ICAR rheometers, the Viskomat XL, the eBT-V, the RheoCAD (two geometries), the 4SCC rheometer (two geometries), the plate test, the sliding pipe rheometer, a tribometer and an interface tool for the ICAR rheometer. This paper describes the mixture design and rationale of the five investigated concrete and three investigated mortar mixtures, design and analysis of the experiments, and comparison of test results. The findings confirmed some of the conclusions from two previous testing campaigns and expanded the findings to more modern concrete mixtures and more diversified sets of rheological devices. The investigated rheometers yielded different absolute values for material parameters, but they all were able to similarly distinguish between mixtures qualitatively. For static yield stress and interface rheology measurements, similar conclusions were obtained as for flow curves.

Interfacial strength between cement paste and an acrylic polymer, Poly(methyl methacrylate) (PMMA) primarily originates from the chemical interactions (formation of metal complex) between calcium ions of the cement paste and the ester functional group of PMMA. There are certain parameters, controllable at a construction site and can potentially influence the calcium characteristics of cement paste substrate, thereby affecting the interfacial strength. It is interesting to examine how these parameters can be engineered to enhance interfacial strength. To this end, the present work investigates the role of calcium on the interfacial strength between cement paste and PMMA by evaluating the influence of various parameters at early (2 days) and later (28 days) days of hydration. The parameters considered were w/c ratio, duration of curing, viscosity of PMMA, and use of lime coating. Macro-mechanical experiments such as slant shear and pull-off adhesion tests were performed to measure interfacial adhesive strength. Further, to understand the mechanism of calcium crosslinking in the absence of calcium ions, the effect of removal of pore solution from cement paste on interfacial strength was investigated. The experimental results indicate that the parameters considered have more influence on interfacial strength when PMMA was coated at the early age of hydration than coated at later ages. The trend observed in the interfacial strength is mainly ascribed to the variation in the concentration of calcium ions available for chemical interaction in the different conditions considered.

In order to efficiently utilize the waste bituminous pavement materials and waste bio-oil, the composition of bio-oil rejuvenator was optimized. The rejuvenation efficiency of the waste bio-oil rejuvenator was evaluated from rheological properties and chemical composition. In addition, a quantitatively evaluation index for the rejuvenation efficiency was proposed. The results show that the central composite design and response surface methodology is effective in optimizing composition of rejuvenators. The dosage of waste bio-oil in the rejuvenated bitumen reached 9%. Compared to another two commercial rejuvenators, waste bio-oil rejuvenator rejuvenated the aged bitumen more effectively. Its rejuvenation efficiency for rheological parameters of aged bitumen was close to 100%. The waste bio-oil rejuvenator restored the performance of aged bitumen by reducing the proportion of macromolecular substances. The rejuvenation efficiency of aromatics, colloidal instability index and carbonyl functional groups were 57.1%, 126.9% and 78.7% respectively.

The combination of environmental actions and mechanical load, which most structural concretes are subjected to, has a synergetic effect on the durability of concrete. The comparative test conducted by RILEM TC 281-CCC WG4 demonstrated and quantified the effect of an applied mechanical load on carbonation performance of concrete with supplementary cementitious materials. Although the effect of loading on the chemical durability of concrete should be taken into consideration for the development of realistic service life predictions, they have been widely overlooked so far. This recommendation proposed by RILEM TC 281-CCC WG4 proposes a testing method for determining the effect of applied load on the carbonation rate of concrete. It specifies a detailed experimental procedure to determine the carbonation development of concretes subjected to compressive and tensile loads. Therefore this recommendation will support the consideration of such combined effects in design codes.

It is believed that many historic mortars were made using hot-lime mixing techniques. They are back in use today, and their good qualities are often praised, including being more compatible and a better match with historic fabrics. This paper studies the methods of producing hot-lime mortars and putties. It discusses the variables that determine the properties of the resultant mortars such as slaking and calcination, and compares hot-lime mortars with their equivalent putties, and with factory-produced calcium lime and hydraulic lime mortars. The paper concludes that the most important variable that governs the properties of hot-lime mixed mortars is the quantity of water used for slaking, because it determines the temperature reached during slaking which makes the resultant Ca(OH)2 vary from a fairly large size to extremely small, hence producing mortars with different properties. Based on scientific and historic evidence, it is concluded that the best method for hot-lime mixing is dry-slaking (sand-slaking) with long storage, because it combines a high slaking temperature (that reduces particle size and increases the surface area of the hydrate), with gradual slaking (that lowers volume expansion and crack development) and long storage (to ensure complete slaking hence no expansion cracks). Many historic mortars were probably hot-lime mixed. However, it is practically impossible to recreate them today due to the different limestones, kilns, calcination regimes and slaking/storage methods used in the past. Hydraulic and magnesian quicklimes were used historically for hot-mixing. In contrast, most of the factory quicklimes used today are purer limes with higher free lime content and a greater reactivity. Therefore, a hot-lime mix made with a factory-produced quicklime may not be more authentic or compatible than a natural hydraulic lime –NHL– mortar designed to suit a specific fabric and application. To ensure quality mortars that can be consistently repeated, a hot-lime mixing specification should contain both the process and the materials including: type of slaking (dry/wet); amount of water used; mixing details and the time at which it takes place; storage time and at what stage does it occur. To control the slaking temperature, the right amount of water should be established (according to free lime content) by trial which will also inform on the amount of yield and hence allow proportioning. With careful site work and specification, high-quality, compatible mortars can be made with both NHLs and hot-lime mixing. However hot-lime mixing requires more time and logistics, closer care and a more complicated specification.

To understand the general coupled chemo-thermo-hydro-mechanical (CTHM) behavior of CSRE, this work reviews the cement hydration process in CSRE and its influence on the thermo-hydro-mechanical (THM) behaviors of CSRE materials. It has been observed that the unconfined compressive strength of CSRE increases with material dry density. Compared to other factors such as grain size distribution, dry density, and water content, the effect of cement hydration on the variations of the soil water retention curve (saturation-suction scale) and thermal conductivity is not significant. The free water consumed in the hydration process exists in the form of chemically reacted water and gel water. Moreover, cement hydration increases the mechanical resistance of CSRE over time and is influenced by the curing conditions. The characteristics of CSRE vary considerably among different experimental works reported in the literature. The combined effect of initial water content, initial dry density, initial grain size distribution, initial cement content, curing conditions and curing time needs to be considered together from the design stage of CSRE material. The lack of a global view of all types of CSRE materials poses great difficulties in making a worldwide acceptable standard for CSRE materials. Consequently, based on the experimental results from literature review, a finite element numerical framework is proposed to reproduce a typical CSRE material as well as to globally explain the complex coupled CTHM properties of CSRE from the design stage.

In Brittany, invasive algae represent a real problem, unbalancing local ecosystems and threatening the economy and tourism, with massive stranding’s, especially in summer. The valorization of invasive algae in green processes and materials such as ecological building materials could represent a real opportunity to try to control the spread of these species. Raw earth is a locally sourced building material, non-toxic and sustainable. In this work, we propose then to compare the effect of four invasive Brittany seaweeds, exotic or indigenous, on the fresh state and hardened properties of raw earth material. In particular, we investigated the performance of Polyopes lancifolius, Solieria chordalis, Ulva sp. and Sargassum muticum on the compressive strength, water resistance and extrudability of the raw earth material. Several forms of seaweed extracts were tested, raw seaweeds dried and ground, freeze-dried hot water extracts and extracted polysaccharides. Our results showed that the incorporation of S. chordalis and S. muticum, in the freeze-dried form or polysaccharides, allows a threefold increase in the compressive strength and a better resistance to water.

The use of high-strength and highly flexible wire ropes as internal shear reinforcement may be a solution to reduce the congestion of steel reinforcements and facilitate their installation in reinforced concrete (RC) elements. This paper aims to study the effectiveness of continuous wire ropes in substituting traditional shear reinforcement and its effect on the RC beam’s shear behavior. Four-point bending tests were performed on 32 beam specimens. Fourteen different configurations of shear reinforcement were tested, of which four were reinforced in a conventional manner and ten with wire ropes. Deflection and crack opening were measured using Digital Image Correlation (DIC) technique. Test results show that the experimental shear capacities of beams with wire ropes are in good agreement with the estimated theoretical values. The difference in behavior of the two types of beams—transversely reinforced with wire ropes or traditional steel rebars—occurs at the appearance of the first diagonal crack. A progressive evolution of the crack opening occurs when using traditional rebars, while a sudden crack opening accompanied by loss of shear strength occurs in beams reinforced with wire ropes. This sudden loss is repeated several times during the test before reaching the final failure drop. The conjunction of two phenomena may be at the origin of this difference in the beam behavior: the smooth stiffness of the wire rope under tensile stresses associated with a weak wire rope-concrete bond.

In this study, the fresh state and hydration properties of 0–60% lithium slag blended cement pastes were investigated at water-binder ratio of 0.47. The workability of the fresh pastes was evaluated by measuring the air content, marsh cone flow, mini-slump flow, setting times, and through rheology tests. A 40% lithium slag cement could produce 91% strength activity index at 28 days; mini-slump pat diameter of 70.54 mm; marsh cone flow efflux time of 145 s; air content 0.6%; hydration heat of 300 J/g (at 72 h). At replacement levels above 40%, the strength activity index, air content, mini-slump flow, hydration heat, and fluidity were significantly reduced. Experimental investigations confirm that the mini-slump test provides the best correlation coefficients (R2 = 0.96) with the maximum shear viscosity of lithium slag cement pastes than the marsh cone flow efflux time and air content. The classical slump and rheological models were used to characterise the mini-slump, yield stress, and plastic viscosity of low to high volume lithium slag cement pastes. The present study recommends that a 40% lithium slag cement paste is a viable option to produce green concrete for optimum fresh, hydration, rheological, and hardened properties.

Passing ability is an important property of self-compacting concrete (SCC). Blockage due to poor passing ability leads to the formation of voids, thereby creating weak areas in concrete structure. Moreover, the aggregate morphology greatly influences the passing ability of fresh SCC. In this study, the 3D laser scanning technology and the digital image processing technology were used to quantitatively characterize the aggregate morphology. The aggregate Clump model with natural morphology was generated using the Bubble Pack algorithm. Also, a virtual aggregate database was built, and a 3D discrete element modeling framework for J-Ring test based on the adhesive rolling resistance linear model was proposed. On this basis, the effects of sphericity from 0.5 to 0.9, angularity index from 250 to 650, and rebar spacing from 37.7 to 79.5 mm on the passing ability of SCC were quantitatively analyzed, and the blockage mechanism of SCC was discussed from the meso-scale level. The results show that blockage in SCC is a probabilistic event. The existence of flaky, elongated and multi-angular aggregates increases the possibility of forming granular arches, and the closer the aggregate is to a sphere or the smoother the surface contour, the better the passing ability of fresh SCC. However, when the sphericity index is greater than 0.8, the angularity index is greater than 550, and the rebar spacing is greater than three times the maximum aggregate size, the effect of aggregate morphology or rebar spacing on the passing ability of SCC is not significant.

Thermal cracking has long been a major concern for airport bituminous pavements in cold regions since it is in close connection with the safe operation of aircraft. This study aims to develop a design method for low-temperature performance-oriented airport bituminous mixtures. The research work mainly includes selecting design parameter, establishing design procedure, and verifying design method. The test and analysis results showed that the destructive tensile strain (DTS) of low-temperature splitting test was sensitive to the change of bitumen content, and can accurately characterize the thermal cracking resistance of the bituminous mixtures. Therefore, DTS was suitable as the design parameter, and its critical values were proposed for different climatic conditions. Furthermore, a new design procedure was established by incorporating DTS into the designs of gradation and optimum bitumen content. Through tests under different low temperature environments, it was verified that the design method can significantly improve the anti-cracking ability of designed bituminous mixtures. This study provides a new idea for enhancing the thermal cracking resistance of airport bituminous pavements in cold regions in terms of bituminous mixture design.

Red mud (RM) is a kind of solid waste by the production of alumina. Long-term storage of RM can occupy a large amount of land and cause serious pollution to soil, air and water. Alkali activated cementitious material (AACM) is a new type of green environmental protection material, which provides a new idea for the efficient use of RM. In this research, RM is thermally activated and mixed with ground granulated blast-furnace slag (GGBFS) and alkali activator to prepare AACM. In order to improve the performance of this AACM, the influence of activator content and type on the chemical shrinkage and mechanical property of the AACM were studied and discussed comprehensively. The obtained results show that the used RM shows best activity after calcined at 700 °C; the suitable ratio of RM to GGBFS is 5:5. Water glass has better activation effect on the AACM made with RM and GGBFS than calcium hydroxide (Ca(OH)2). But, the use of water glass and Ca(OH)2 together is more appropriate for this AACM. The strength of the AACM activated by 20 wt% Ca(OH)2 and 20 wt% water glass can reach 88 MPa at 120 days.