Impact of Wetting–Drying Cycles on the Mechanical Properties and Microstructure of Wood Waste–Gypsum Composites

Large amounts of wood waste are generated each year in the world. In an attempt to identify a good recovery option for those residues, wood waste from construction and demolition works were used as raw materials in gypsum plasters. However, wood is a biodegradable material which implies that the products or materials that contain it are susceptible to su ering an important deterioration, due to exposure in certain environments. For that reason, the aim of this work was to simulate the e ects that, in the long term, the atmospheric exposure of wood waste–gypsum composites would have. To do that, the plasters were subjected to 5, 10, and 15 wetting–drying cycles in a climatic chamber. In this study, the density, flexural and compressive strength, and ultrasonic velocity of these composites were determined by the influence of the aging process on their mechanical properties. Furthermore, in order to detect changes on their internal structure, scanning electron microscopy tests (SEM) were used. The results showed that they were suitable to be used as indoor coverings of buildings. However, a treatment to reduce the moisture absorption of the wood waste must be studied if mixtures with high percentages of wood shavings (WS20) are used in wet rooms

Use of reinforced inorganic cement materials for spark wire and drift chamber wire frames

The results of a survey, materials test, and analysis study directed toward the development of an inorganic glass-fiber reinforced cement material for use in the construction of space qualified spark wire frames and drift chamber frames are presented. The purpose for this research was to evaluate the feasibility of using glass fiber reinforced cement (GFRC) for large dimensioned structural frames for supporting a number of precisely located spark wires in multiple planes. A survey of the current state of the art in fiber reinforced cement materials was made; material sample mixes were made and tested to determine their laboratory performances. Tests conducted on sample materials showed that compressive and flexural strengths of this material could approach values which would enable fabrication of structural spark wire frames

Hierarchically structured composites and porous materials

This thesis develops a hydrogel bead templating technique for the preparation of hierarchically structured composites and porous materials. This method involves using slurries of hydrogel beads with different size distributions as templates. Mixing hydrogel beads with a scaffolding material and then allowing the scaffold to harden, followed by drying of the composite leaves pores in the place of the hydrogel beads. These pores reflect the size and shape of the templates used and the porosity reflects the volume percentage of hydrogel bead slurry mixed with the scaffolding material. A viscous trapping technique has been developed which utilises the viscosity of methylcellulose to stop sedimentation of the scaffold particles during network formation. Both of these methods are attractive due to being cheap, non-toxic and they use food grade materials which allows their use in a multitude of applications.Porous and hierarchically porous gypsum composites have been prepared using both hydrogel bead templating and viscous trapping techniques, or a combination of the two. The level of control over the final microstructure of the dried composites offered by these techniques allowed for a systematic investigation of their thermal and mechanical properties as a function of the pore size, porosity and hierarchical microstructure. It has been shown that the thermal conductivity decreases linearly with increasing porosity, however it was not dependent on the pore sizes that were investigated here. The mechanical properties, however, were significantly different. The porous composites produced with either small hydrogel beads (100 μm) or methylcellulose solution had approximately twice the compressional strength and Young’s modulus compared to the ones produced with large hydrogel beads (600 μm).The sound insulating properties of porous and hierarchically porous gypsum composites have also been investigated. With increasing porosity, the sound transmission loss decreases, as expected. At constant porosity, it is shown that the composites with large pores perform significantly better than the ones with small pores in the frequency range of 75-2000 Hz. At higher frequencies (>2400 Hz) the composites with smaller pores begin to perform better. The material’s microstructure has been studied in an attempt to explain this effect.The hydrogel templating technique can be used to prepare composite materials if the drying step is not performed. Hydrogel beads have been incorporated into a soap matrix. The dissolution rate of these composites as a function of hydrogel bead size and volume percentage of hydrogel beads incorporated within the soap matrix has been investigated. It has been shown that the dissolution rate can be increased by increasing the volume percentage of hydrogel beads used during composite preparation but it is independent on their size distribution. Finally, three methods of controlling the release rate of encapsulated species from these soap-hydrogel bead composites have been shown. The first method involved varying the size distribution of the hydrogel beads incorporated within the soap matrix. The second involved changing the concentration of the gelling polymer and the final method required co-encapsulation of an oppositely charged polyelectrolyte.A binary hydrogel system has been developed and its rheological and thermal properties have been investigated. It consists of agar and methylcellulose and shows significantly improved rheological properties at high temperatures compared to agar alone. The storage modulus of the two component hydrogel shows a maximum at 55 °C which was explained by a sol-gel phase transition of methylcellulose, evidence of which was seen during differential scanning calorimetry measurements. After exposure of this binary hydrogel to high temperatures above the melting point of agar alone (> 120 °C), it maintains its structure. This suggests it could be used for high temperature templating or structuring of food products.The melt-resistant binary hydrogel was used for the preparation of pancake-hydrogel composites using hydrogel bead templating. Mixing slurry of hydrogel beads of this composition with pancake batter, followed by preparation at high temperatures produced pancakes with hydrogel beads incorporated within. Bomb calorimetry measurements showed that the caloric density could be reduced by a controlled amount by varying the volume percentage of hydrogel beads used during preparation of the composites. This method could be applied to other food products such as biscuits, waffles and breakfast bars. Furthermore, there is scope for development of this method by the encapsulation of flavour enhancing or nutritionally beneficial ingredients within the hydrogel beads

Study on sisal fibres as insulator in building materials

In this current era, there are some concerns of using synthetic fibres in regards to their impact on the environment since they are non-recyclable and non degradable. There are many attempts by various groups of engineers and researchers to use natural fibres in engineering applications, in the hopes of replacing synthetic fibres with natural fibres. In this project, the possibility of using natural fibres in building materials is investigated in terms of their compression strength and heat conductivity. Sisal fibres are selected as reinforcement for gypsum walls for the application in industrial and commercial buildings. To gain high interfacial adhesion of the sisal fibres with gypsum, a study on the optimum chemical treatment concentration of NaOH (0-10 %) is considered. To study the heat conductivity of the composites, a newly designed heat conductivity test setup is developed to study the influence of different volume fractions of glass and sisal fibres on the conductivity of gypsum. In addition, compressive test was performed for the selected materials. Failure mechanisms of the samples after compressive testing are examined with the aid of the scanning electron microscopy (SEM). The results revealed that the alkalization on the sisal fibres have provided different levels of interfacial adhesion in the composites which were pronounced on the surface topography of the fibres. Based on this observation and supported by other literatures, 6% NaOH was selected as the optimal concentration for composite fabrication. From the compressive test, it was observed that the addition of fibres to the gypsum matrix improves the compressive strength and resulted in reduced brittleness. For sisal fibre-gypsum composite, the optimum fibre content is at 25 vol.% while for glass fibre-gypsum composite, the optimum fibre content is at 30 vol.%. The thermal conductivity resulted showed that pure gypsum was found to have the highest thermal conductivity. The thermal conductivity of the composites decrease with the increment of fibre volume fraction for both synthetic and natural addition of the fibres. Sisal fibre-gypsum composites performs slightly better at insulating heat as compared to glass fibre-gypsum composites possibly due to its porous nature, as heat transfer is impeded by the presence of air voids

Mechanical, structural and microstructural investigations of a novel concrete for special structural applications

Degradation of concrete members exposed to sulphuric acid environments is a key durability issue that affects the life cycle performance and maintenance costs of civil infrastructures. Groundwater, chemical waste, sulphur bearing compounds in backfill, acid rain in industrial zones and biogenic acid in sewage systems are the main sources of sulphuric acid affecting concrete structures. In this research, as part of an ongoing research on development of novel concretes for special applications, an acid resistant mortar (ARM) with current applications in lining and repair purposes was converted to acid resistant concrete in the laboratory and investigated for structural applications in acidic environments. Mechanical properties of the initial acid resistant mortar material, this novel acid resistant concrete (ARC) and a type of conventional concrete (CC), as the control, have been studied in the laboratory subjected to an accelerated test, 7% (by volume) sulphuric acid. The studied mechanical properties included compressive strength, modulus of elasticity (MOE), modulus of rupture (MOR) and indirect tensile strength tests. Apart from acid resistance experiments, other important properties for a structural concrete such as drying shrinkage and concrete performance subjected to high rate strain loads and elevated temperatures were also evaluated for ARC and CC. Structural performance of reinforced concrete (RC) flexural members made of this new concrete (ARC) and CC was assessed before and after different periods of continuous immersion in 7% sulphuric acid solution through static and cyclic loading under four-point bending tests to detect the effects of acid attack on structural performance of RC beams. Load- deflection behaviour, curvature- moment resistance at mid span, ultimate load capacity, ductility factor, stiffness degradation, dissipated energy and damping ratio were the main variables studied in these experiments. Application of ARC in beam-column joints, as another application for this concrete was also investigated due to possessing higher ductility than conventional concrete in mechanical properties tests aiming at reduction of transverse reinforcing bars in such members and the potential for seismic applications. Structural elements (i.e., beams and joints) were also modelled by using FE software ATENA to analyse the experimental results numerically. Microstructural characterisation was also performed on ARC and CC samples before and after acid exposure using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray mapping (XRM) and X-ray diffraction (XRD) to gain a better understanding regarding the change of microstructure of materials after exposure to acid. ARC showed superior performance than CC after exposure to acid in terms of loss of mechanical properties. Structural performance of ARC has been comparable to CC before exposure to acid and after a long period of exposure to acid it showed better performance than CC, particularly in terms of load bearing capacity. The application of ARC in beam-column joints allowed reducing transverse reinforcing bars in these joints (50% compared to CC). Microstructural characterisation also revealed significant facts regarding the deterioration mechanism in both types of concretes and their effect on mechanical properties

Characterization and chromatic evaluation of gypsum-based pastes for construction and heritage restoration

The authors would like to thank the reviewers for their thoughtful comments and efforts towards improving our manuscript.This work was supported by the REMINE Programme for Research and Innovation Horizon 2020 Marie Sklodowska-Curie Actions and RRRMAKER H2020-MSCA-RISE-2020 (Marie Sklodowska-Curie Research and Innovation Staff Exchange and was carried out under the auspices of Research Groups RNM 0179 and HUM 629 of the Junta de Andalucia. Funding for open access charge: Universidad de Granada/CBUAThis research evaluates the chromatic behavior of gypsum-based pastes containing added pigments which enable their use in both new construction projects as well as in restoration interventions for built heritage. Furthermore, the impact of adding pigments to the aforementioned material after twenty-eight and ninety days has also been studied. This was confirmed by carrying out compositional, mineralogical and physical studies of the raw materials and the pastes. The results indicate that all of the pastes studied have suitable mechanical strength values for the type of pastes studied, thereby confirming their suitability for on-site use based on their characteristics and behavior. Colorimetric analysis showed color variations that were clearly perceptible to the human eye, related to increases in luminosity which significantly exceeded 100%, and also to saturation losses featuring percentage variations of more than 100% on assessment after ninety days. This colorimetric analysis by means of quantitative spectrophotometry is of vital importance when determining the loss of color intensity of the pastes used, since subjective observation results in serious errors of interpretation. This type of study reflects the use of instrumental color measurements for this type of materials and mixtures.REMINE Programme for Research and Innovation Horizon 2020 Marie Sklodowska-Curie ActionsRRRMAKER H2020-MSCA-RISE-2020 (Marie Sklodowska-Curie Research and Innovation Staff ExchangeJunta de Andalucia RNM 0179 HUM 629Universidad de Granada/CBU

Synergistic and Environmental Benefits of Using Cement Kiln Dust With Slag and Fly Ash in Cemented Paste Tailings

Many researchers have validated the phenomenon of internal sulphate attack in ordinary Portland cement (CSA Type GU) based cemented paste tailings containing sulphide minerals and have observed secondary gypsum as an ubiquitous phase in such matrices. The secondary gypsum, due to its soft nature and swelling and expansive properties, is principally considered to be the sole culprit responsible for subsequent internal cracking and strength degradation of sulphidic paste at later stages. High Portland cement cost and its apparent poor performance in the long-term in sulphate rich environments advocate for the formulation of resilient cemented paste tailings using economical but efficient binders. This study demonstrates the effectual utilization of selective cement kiln dusts (CKDs) in composite binder systems containing ground granulated blast furnace slag (SL), Type C fly ash (FC) and a small amount of Portland cement. The addition of calcium and alkali rich cement kiln dust in Portland cement-slag and Portland cement-fly ash binder systems functioned as an excellent alkaline activator and accelerator in promoting the hydration mechanisms within cemented paste tailings formulations. High alkaline pore solution created by free calcium rich cement kiln dust (CKD) is capable of disintegrating the solid glassy network of supplementary cementing materials to produce reactive silicate and aluminate compounds. Comparative assessment of a range of binder combinations has been carried out for cemented paste tailings formulations using performance assessment indicators such as unconfined compressive strength, saturated hydraulic conductivity, micro-structure, and contaminant containment capability (leachability). The short-and long-term performance evaluation of the unconfined compressive strength of blended cements in cemented pastes of sulphidic tailings was carried out over a curing period of 480 days. Cement kiln dusts (DA and DH) containing high CaO content (52.4% and 57.8%, respectively) and low Loss on Ignition (LOI), i.e., 5.1% and 4.8%, respectively, performed best in making cemented paste tailings, whereas the paste mixtures containing DB and DL (with very low free lime and very high LOI) as single binders in combination with mine tailings (MT) never hardened. The addition of selective CKD, and SL, and/or FC as partial replacement for Portland cement can improve the performance of the cemented paste tailings containing sulphide minerals and alleviate the strength loss associated with Type GU cement based paste. The behavior is attributed to the latent strength acquisition of SL and FC in the blended cements containing DA and DH as a result of proliferating hydration and augmented pozzolanic reactivity. Previous studies carried out by other researchers on hardened cemented paste tailings specimens containing Portland cement-pozzolans binders confirmed the possibility of the presence of un-reacted or un-hydrated particles of slag and fly ash in such matrices. In the present study, SEM was carried out on cemented paste tailings samples to investigate the effect of using calcium and alkali rich CKD on pozzolanic reactivity of binders containing SL and FC. The effect of incorporation of DA or DH in GU/HS-SL and GU/HS-FC binders was analyzed in high magnification modes. No un-reacted grains of SL and/or FC were found within the crushed surfaces of the matrices. The glassy SL was completely disintegrated by the highly alkaline pore solution when attacked by OH- ions. As well, all the amount of FC used in composite binder system was completely exhausted by the accelerated pozzolanic activity. Concomitantly, the observed microstructure delineation of selected cemented paste tailings samples was found to be well acquiescent with their respective mechanical performance (based on the unconfined compressive strength). The precipitation of calcium hydroxide in Type GU based cemented paste tailings can be inadequate for total blocking of pores within cemented paste tailings matrix. The enhanced pozzolanic reactivity of SL and FC with additional calcium hydroxide produced by the incorporation of high calcium and alkali rich CKD in cemented tailings matrices generated additional hydration products, favoring enhanced pore refinement and densification, which, in turn, reduced the transportability of fluid through the hardened matrices. Meticulous geochemical characterization of cemented paste tailings formulations is imperative, particularly when binders replace the traditional Portland cement. The leaching behavior of metals in cemented paste tailings formulations was studied using field mimicking leaching protocols to obtain information on the fixation involving both chemical stabilization and physical encapsulation mechanisms. Leaching test results based on the Synthetic Precipitation Leaching Procedure (US EPA Method 1312) showed that cemented paste tailings formulated with Type GU cement alone are susceptible to contaminant leaching and, therefore, do not eliminate interaction between the monolith and contact waters. On the other hand, optimized cementing blends containing a small amount of Type GU cement and SL activated by DH offer more efficient contaminant fixation capabilities for tailings pastes. Low calcium cement kiln dust (DL) promoted chemical stabilization only within the resultant composites due to lack of cementitious properties and is, therefore, incapable of providing physical encapsulation of the contaminants. The results advocate the technically beneficial synergy of composite binders containing selective CKDs for paste preparation in contrast with Portland cement alone, Portland cement-slag, and Portland cement-fly ash binder systems in sulphidic mine tailings management. An optimized mix proportion is however required to achieve optimal performance