Bradford Scholars is the University of Bradford online research archive. Access is free to anyone interested in research being conducted at Bradford. In the repository you will find a range of materials from journal articles and conference papers to research reports and theses.

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  • Assessment of lime-treated clays under different environmental conditions

    Mohamed, Mostafa H.A.; Ali, Hatim F.A. (University of BradfordFaculty of Engineering and Informatics, 2019)
    Natural soils in work-sites are sometimes detrimental to the construction of engineering projects. Problematic soils such as soft and expansive soils are a real source of concern to the long-term stability of structures if care is not taken. Expansive soils could generate immense distress due to their volume change in response to a slight change in their water content. On the other hand, soft soils are characterised by their low shear strength and poor workability. In earthwork, replacing these soils is sometimes economically and sustainably unjustifiable in particular if they can be stabilised to improve their behaviour. Several techniques have evolved to enable construction on problematic soils such as reinforcement using fibre and planar layers and piled reinforced embankments. Chemical treatment using, e.g. lime and/or cement is an alternative method to seize the volume change of swelling clays. The use of lime as a binding agent is becoming a popular method due to its abundant availability and cost-effectiveness. When mixed with swelling clays, lime enhances the mechanical properties, workability and reduces sensitivity to absorption and release of water. There is a consensus in the literature about the primary mechanisms, namely cation exchange, flocculation and pozzolanic reaction, which cause the changes in the soil characteristics after adding lime in the presence of water. The dispute is about whether these mechanisms occur in a sequential or synchronous manner. More precisely, the controversy concerns the formation of cementitious compounds in the pozzolanic reaction, whether it starts directly or after the cation exchange and flocculation are completed. The current study aims to monitor the signs of the formation of such compounds using a geotechnical approach. In this context, the effect of delayed compaction, lime content, mineralogy composition, curing time and environmental temperature on the properties of lime-treated clays were investigated. The compaction, swelling and permeability, and unconfind compression strength tests were chosen to evaluate such effect. In general, the results of the geotechnical approach have been characterised by their scattering. The sources of this dispersion are numerous and include sampling methods, pulverisation degree, mixing times and delay of compaction process, a pre-test temperature and humidity, differences in dry unit weight values, and testing methods. Therefore, in the current study, several precautions have been set to reduce the scattering in the results of such tests so that they can be used efficiently to monitor the evolution in the properties that are directly related to the formation and development of cementitious compounds. Four clays with different mineralogy compositions, covering a wide range of liquid limits, were chosen. The mechanical and hydraulic behaviour of such clays that had been treated by various concentrations of lime up to 25% at two ambient temperatures of 20 and 40oC were monitored for various curing times. The results indicated that the timing of the onset of changes in mechanical and hydraulic properties that are related to the formation of cementitious compounds depends on the mineralogy composition of treated clay and ambient temperature. Moreover, at a given temperature, the continuity of such changes in the characteristics of a given lime-treated clay depends on the lime availability.
  • Dynamic soil-structure interaction of reinforced concrete buried structures under the effect of dynamic loads using soil reinforcement new technologies. Soil-structure interaction of buried rigid and flexible pipes under geogrid-reinforced soil subjected to cyclic loads

    Mohamed, Mostafa H.A.; Sheehan, Therese; Elshesheny, Ahmed M.M. (University of BradfordFaculty of Engineering and Informatics University of Bradford, 2019)
    Recent developments in constructions have heightened the need for protecting existing buried infrastructure. New roads and buildings may be constructed over already existing buried infrastructures e.g. buried utility pipes, leading to excessive loads threatening their stability and longevity. Additionally applied loads over water mains led to catastrophic damage, which result in severe damage to the infrastructure surrounding these mains. Therefore, providing protection to these existing buried infrastructure against increased loads due to new constructions is important and necessary. In this research, a solution was proposed and assessed, where the protection concept would be achieved through the inclusion process of geogrid-reinforcing layers in the soil cover above the buried infrastructure. The controlling parameters for the inclusion of geogrid-reinforcing layers was assessed experimentally and numerically. Twenty-three laboratory tests were conducted on buried flexible and rigid pipes under unreinforced and geogrid-reinforced sand beds. All the investigated systems were subjected to incrementally increasing cyclic loading, where the contribution of varying the burial depth of the pipe and the number of the geogrid-reinforcing layers on the overall behaviour of the systems was investigated. To further investigate the contribution of the controlling parameters in the pipe-soil systems performance, thirty-five numerical models were performed using Abaqus software. The contribution of increasing the amplitude of the applied cyclic loading, the number of the geogrid-reinforcing layers, the burial depth of the pipe and the unit-weight of the backfill soil was investigated numerically. The inclusion of the geogrid-reinforcing layers in the investigated pipe-soil systems had a significant influence on decreasing the transferred pressure to the crown of the pipe, generated strains along its crown, invert and spring-line, and its deformation, where reinforcing-layers sustained tensile strains. Concerning rigid pipes, the inclusion of the reinforcing-layers controlled the rebound that occurred in their invert deformation. With respect to the numerical investigation, increasing the number of the reinforcing-layers, the burial depth of the pipe and the unit-weight of the backfill soil had positive effect in decreasing the generated deformations, stresses and strains in the system, until reaching an optimum value for each parameter. Increasing the amplitude of the applied loading profile resulted in remarkable increase in the deformations, stresses and strains generated in the system. Moreover, the location of the maximum tensile strain generated in the soil was varied, as well as the reinforcing-layer, which suffered the maximum tensile strain.
  • Long-chain branched poly(lactic acid)- b-poly(lactide- co-caprolactone): Structure, viscoelastic behavior, and triple-shape memory effect as smart bone fixation material

    Liu, Y.; Cao, H.; Ye, L.; Coates, Philip D.; Caton-Rose, Philip D.; Zhao, X. (2020-03-11)
    A novel fully biosbased poly(lactic acid)-b-poly(lactide-co-caprolactone) (PLA-b-PLCL) with a two-phase structure and long-chain branches was specifically designed and prepared through reactive melt processing. The results showed that PLCL segments were introduced onto PLA chains successfully. With the increase of PLCL content, the blockier distribution of LA/CL chain sequences of the sample was exhibited. PLA-b-PLCL showed two distinct thermal transitions, corresponding to the glass transition of PLA and PLCL domains, respectively, whereas the phase morphology changed from a sea-island to a co-continuous structure with increasing PLCL content. Because of the long-chain branched structure, PLA-b-PLCL samples showed a much higher viscoelasticity, strong molecular entanglement, and obvious strain-hardening behavior, resulting in a high draw ratio of the sample during orientation process, whereas the tensile strength and the modulus of the oriented sample reached up to 173 MPa and 5.4 GPa, respectively, which basically met the requirements of bone screws. Moreover, PLA-b-PLCL showed a triple-shape memory effect at 55 and 120 °C, respectively. For PLA-b-30 wt % PLCL, the recovery ratio can reach up to 98.1% under 55 °C, while high mechanical properties can be maintained, realizing self-reinforcement and self-fastening effect simultaneously as a smart bone fixation material.
  • Suppressed cavitation in die-drawn isotactic polypropylene

    Lyu, D.; Sun, Y.; Lu, Y.; Liu, L.; Chen, R.; Thompson, Glen P.; Caton-Rose, Philip D.; Coates, Philip D.; Wang, Y.; Men, Y. (2020-06)
    Cavitation is an important phenomenon in solid-phase deformation of polymers, which either has potential adverse effects on physical properties or creates potential opportunities for new properties. In either case, it needs to be better understood to help achieve better control of cavitation and its effects. Cavitation associated with solid-phase deformation in a β-nucleated isotactic polypropylene was found to depend on the solid-phase deformation route employed. Compared with samples obtained by free tensile stretching, cavitation was suppressed in samples deformed via die-drawing, although an almost identical β-to α-phase transition was observed for both deformation routes. Even when die-drawn samples were subsequently deformed to large strains by free stretching, there was still no comparable cavitation compared with the single free tensile-stretching route. The die-drawing process appears to suppress cavitation by fundamentally diminishing the number of growable nuclei of cavities, rather than merely hindering the growth of cavities. A relationship between cavitation intensity and the fractions of lamellae along specific directions has been established. During subsequent free stretching of die-drawn samples, newly created cavities were suggested to be initiated within the crystalline layers. The reduction of the cavity nuclei in the die-drawing process originated from the stabilization of the connections between the crystalline blocks within the lamellae.
  • Experimental analysis of the tensile property of FFF-printed elastomers

    Lin, X.; Coates, Philip D.; Hebda, Michael; Wang, R.; Lu, Y.; Zhang, L. (2020-10)
    Designing and manufacturing functional parts with enhanced mechanical property is a major goal of fused filament fabrication (FFF) for polymeric elastomers, which exhibits major advantages in producing such parts with a range of structures. But the unsatisfactory mechanical performance constrains greatly its real application and there is yet no consensus in the mechanical characterization of printed samples. This work takes the nozzle height as the considered factor and tests the tensile property of FFF-printed thermoplastic polyurethane (TPU). Rheological property of the TPU melt, represented here by die swell behavior and shear viscosity, were measured initially to obtain a preliminary assessment of the material suitability and an optimization of melt extrusion conditions for FFF processing. Then correlation between the cross-section profile of deposited bead and the tensile performance of printed sample were evaluated. Both the shape of deposited bead and the bonding strength of two adjacent beads are emphasized when explaining the measured tensile strength. The significance of molecular permeation efficiency at bead-bead interfaces, and bonding-releasing patterns between adjacent beads to the tensile failure of printed objects is discussed.

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