1,721,364 research outputs found
Mechanical performance of different stabilised soils for application in stratified ground
No full textTo achieve homogeneity in soil mixing along the depth of a column in a non-homogeneous layered soils, it is necessary to understand the effect of soil type on the treatment and to adapt the treatment for the different soil strata. For this purpose, an extensive laboratory testing programme was carried out to examine the effect of different soils and cement content on the mechanical and physical properties of the resulting treated soils. Four different soils, namely gravely sand; silty clayey gravely sand, silty clay and a pure clay were tested. Different grout constituents, constituent ratios, dosages and water content were used in order to improve the performances of the mixes using Portland cement as the main binder. The tests performed included unconfined compressive strength, from which the elastic stiffness was also calculated, and permeability at 28 days. The results show that relatively homogenous results in terms of compressive strength and permeability may be reached by modifying the cement-bentonite ratio in granular soils and the binder dosage in fine-grained soils. The results constitute a preliminary useful guide to adapt in the construction techniques in field applications
Influence of curing temperature on the strength of cement stabilised artificial clays
No full textThe paper present results of a laboratory investigation on the influence of curing temperature and time on the mechanical characterisation of cement-stabilised clays as used in deep soil mix applications. Numerical modelling, based on the Arrhenius equation, is also presented. Experimentally, this model was applied to a series of tests performed at different temperatures. For each temperature, unconfined compressive strength tests were performed at specific time intervals in order to follow the curing and the increase of strength with time. The clay used was artificial clay made up of 40% kaolin clay and 60% of silt (using silica flour). Three different water contents were used to compare the performance of different soft clays. The results showed that the strength increases with the temperature. It was also found that the activation energy is the same for all three water content clays. Using the numerical modelling long-term behaviour of up to 2.4 years was predicted
Influence of moulding procedure, curing temperature and mixing time on the strength of cement stabilised artificial clays
No full textStrain Monitoring of Concrete Using Carbon Black-Based Smart Coatings
Full text linkGiven the challenges we face of an ageing infrastructure and insufficient maintenance, there is a critical shift towards preventive and predictive maintenance in construction. Self-sensing cement-based materials have drawn interest in this sector due to their high monitoring performance and durability compared to electronic sensors. While bulk applications have been well-discussed within this field, several challenges exist in their implementation for practical applications, such as poor workability and high manufacturing costs at larger volumes. This paper discusses the development of smart carbon-based cementitious coatings for strain monitoring of concrete substrates under flexural loading. This work presents a physical, electrical, and electromechanical investigation of sensing coatings with varying carbon black (CB) concentrations along with the geometric optimisation of the sensor design. The optimal strain-sensing performance, 55.5 ± 2.7, was obtained for coatings with 2 wt% of conductive filler, 3 mm thickness, and a gauge length of 60 mm. The results demonstrate the potential of applying smart coatings with carbon black addition for concrete strain monitoring
Impermeabilization of carbon black-based smart coatings for strain-sensing purposes
Full text linkThis study explores self-sensing properties in carbon black (CB)-based cementitious coatings, focusing on the influence of internal moisture on electrical measurements. Various saturation levels were examined by gradually drying the coatings and encapsulating them with epoxy resin to shield them from external humidity. Results show that inner water impacts the strain-sensing response of the coating, reaching an optimal moisture saturation of 25 % where an equilibrium between carbon black particles, water, and free ions was attained. For coatings on tension surfaces of concrete beams under flexural loads, 230.7 +/- 25.8 was the obtained gauge factor for 3 wt% added carbon black. Epoxy-sealing reduced the bonding strength between the coating and the substrate by 27 %. Nonetheless, epoxy-encapsulated coatings with 3 wt% carbon black achieved a gauge factor of 110.9 +/- 35.5, indicating a promising path for the production and application of self-sensing coatings that remain unaffected by external humidity conditions
Self-healing approaches for the preventive repair of concrete structures: SARCOS COST Action
Full text linkThe SARCOS Action is focused on the preventive repair concept, with the objective of sealing small cracks at the earliest stage of damage, both for new and existing structures, and on looking for standardized methodologies to evaluate the mechanical and durability performance of the treated structures, with continuous feedback from the modelling of self-healing mechanisms. The present contribution aims to give a general vision on the advances achieved within the SARCOS Action, including the revision of the state-of-the-art of the different aspects addressed within the Action: self-healing approaches, techniques for characterizing self-healing performance and self-healing mechanism modelling
Novel production of macrocapsules for self-sealing mortar specimens using stereolithographic 3D printers
Full text linkThe use of capsule-based technology for self-sealing and self-healing cementitious systems has been extensively investigated for both macro-and microencapsulated additions. In this study, macrocapsules, produced using a novel technique were characterised and compared, evaluating mechanical triggering, bonding with the cementitious matrix, and self-sealing efficiency upon integration into cementitious mortar specimens. Macro capsules containing a commercially available water repellent agent were produced in two ways. Stereolithographic additive manufacturing (3D printing) was used to produce novel rigid acrylate macrocapsules as well as alumina ones. Cementitious macrocapsules produced with a rolling technique were also used as a comparison. The capsules were characterised in terms of watertightness, water uptake, and shell morphology. Following this, the capsules were integrated into cement mortar prisms and subjected to controlled cracking by three-point bending to evaluate the triggering and subsequent self-sealing effect. The results highlighted influential process parameters that can be optimised and explored for further capsule-based self-sealing in structural applications
An experimentally based bubble model for clay
No full textIn order to extend the Cam clay model an inner kinematically hardening bubble is added in order to match experimentally observed hysteretic response. The new model is found to be quite successful in reproducing patterns of response observed in slow cyclic oedometer and triaxial tests. -from Author
Self-healing capacity of hardened cement suspensions with high levels of cement substitution
No full textAqueous cement suspensions without aggregates have been commonly applied as a remedial technique in structural and geotechnical applications, often comprising part of the permanent infrastructure. These suspensions derive their mechanical characteristics and properties through the same hydration processes and binding chemistry as concrete; thus they are susceptible to the same deleterious environmental factors and inherent properties. This can endanger the long-term functionality of the installation. Therefore there is a strong incentive of compositional alteration of the basic binder by incorporating supplementary cementitious materials that have been acknowledged to improve the physical properties and enhance the durability characteristics of the hardened matrix. However the latter does not offer a robust long term solution. Therefore a compositional enhancement through biomimetic approach of damage response for the design of high performance cement suspensions is put forward. This study involves two stages, i.e. determination of the autogenous crack sealing behaviour of various optimised blended compositions and the subsequent enhancement of the intrinsic autogenous healing processes through the inclusion of microencapsulated healing agents. Herein the results of this preliminary investigation on the effect of compositional variation on the intrinsic properties of physical response to cracking are presented. Ternary and quaternary blends of minerals -including Portland cement, slag, MgO and silica fume- are being developed and investigated. Upon cracking and water ingress, the unreacted particles are activated and yield hydration products that crystallize in the crack, sealing it off and recovering mechanical characteristics. The self-healing capacity of the samples is quantified through microscope observation, gas permeability test and three-point flexural bending. The findings on the crack healing efficiency and mechanical recovery of initially cracked specimens confirm the existence of self-healing mechanisms in supplementary cementitious materials
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