Image Analysis of Surface Porosity Mortar Containing Processed Spent Bleaching Earth

Image analysis techniques are gaining popularity in the studies of civil engineering materials. However, the current established image analysis methods often require advanced machinery and strict image acquisition procedures which may be challenging in actual construction practices. In this study, we develop a simplified image analysis technique that uses images with only a digital camera and does not have a strict image acquisition regime. Mortar with 10%, 20%, 30%, and 40% pozzolanic material as cement replacement are prepared for the study. The properties of mortar are evaluated with flow table test, compressive strength test, water absorption test, and surface porosity based on the proposed image analysis technique. The experimental results show that mortar specimens with 20% processed spent bleaching earth (PSBE) achieve the highest 28-day compressive strength and lowest water absorption. The quantified image analysis results show accurate representation of mortar quality with 20% PSBE mortar having the lowest porosity. The regression analysis found strong correlations between all experimental data and the compressive strength. Hence, the developed technique is verified to be feasible as supplementary mortar properties for the study of mortar with pozzolanic material

Experimental study on the hydro-mechanical behavior of soils improved using the CSM technology

Deep Mixing Methods (DMMs) can be regarded as constantly evolving technologies for improving soil properties in order to satisfy predefined design requirements. Their applications are very common in geotechnical engineering and, in some cases, they can be conveniently selected instead of more traditional techniques. Despite DMMs are customarily used to strengthen soft soils like peats, clays, and silts, they can also be used very effectively in various subsoil configurations for several purposes, as, for instance, in the case of soil liquefaction prevention or cut-off/retaining walls. Even if soil mixing practice has become very consolidated in geotechnical engineering and numerous researchers in the past have tried to develop predictive equations taking into account the more relevant factors affecting the strength of DM constructions, i.e. influence of binder, soil, mixing and curing conditions, there is still no widely applicable formula for the estimation of the field strength characterized by a reasonable level of accuracy. Predictions are normally based on the mechanical behaviour of laboratory prepared mixtures, which, most of the time, significantly differ from in-situ treated soils due to the specific mixing, curing, and subsoil conditions encountered at the site. Technical standards were recently developed to provide general guidelines for the production of good quality laboratory mixed soil samples. Similarly, other codes concerning the critical deep mixing site construction aspects were introduced in several counties in order to improve the quality assurance and quality control (QA/QC) programmes conceived to verify the treatment effectiveness. However, a direct correlation between laboratory and field mixing performance is still far from being described, probably owing to the lack of a sufficient number of well documented case histories. In this research, a comparison tool between laboratory and field procedures has been tentatively deduced from energetic considerations depending on mixing efforts transferred to the soil to be treated using different devices. This thesis mainly focuses on the results of a comprehensive experimental investigation carried out on treated soil mixtures collected from several worldwide jobsites in which the Cutter Soil Mixing (CSM) technology was used. CSM, launched since 2003, is a recent and efficient system that, besides other DMMs, has the advantage of a high level of process control providing detailed information regarding the in-situ mixing method. The elaboration of these data, which significantly support the usual QA/QC procedures, has been used to define a new easily determinable site parameter closely related to the mixing efficacy, which, in turn, greatly influences the performance attained. As other DM methods, CSM produces some amount of spoil material, which is deemed to contain part of the binder introduced into the soil to activate hydration reactions once combined with both water and minerals in the ground. Since no estimation methods are available to evaluate the binder loss, an approximate amount of binding material is customarily added and mixed with the natural soil, hampering the performance prediction. To remedy this situation, a new formulation has been proposed to estimate the binder loss and to compute a more proper cement content. During the research activity, mechanical, hydraulic, mineralogical, and micro-structural tests were carried out in order to describe in detail the behaviour of the CSM treated material from different points of view and to acquire a reliable picture of the main factors affecting the relevant properties of stabilized soils. The obtained test results allowed to develop a new mathematical model for the evolution of the mechanical strength of granular and cohesive soils treated with the CSM technique as a function of the specific site conditions. The defined procedure has proved to be very effective in the major part of the case histories considered in this work

Development and characterization of cotton and cotton fabric reinforced geopolymer composites

Sustainable geopolymer composites reinforced with natural cotton fibres have been developed and their mechanical and durability properties are evaluated in this research. Results showed that the mechanical properties (flexural strength, flexural modulus, fracture toughness, compressive strength, impact strength and hardness) of woven cotton fabric-reinforced geopolymer composites were superior to those of geopolymer composites with short cotton fibres. Exposure to water and elevated temperatures (200 to 1000°C) severely reduced the mechanical properties of the composites

Trends and Prospects in Geotechnics

The Special Issue book presents some works considered innovative in the field of geotechnics and whose practical application may occur in the near future. This collection of twelve papers, in addition to their scientific merit, addresses some of the current and future challenges in geotechnics. The published papers cover a wide range of emerging topics with a specific focus on the research, design, construction, and performance of geotechnical works. These works are expected to inspire the development of geotechnics, contributing to the future construction of more resilient and sustainable geotechnical structures

Numerical modelling of additive manufacturing process for stainless steel tension testing samples

Nowadays additive manufacturing (AM) technologies including 3D printing grow rapidly and they are expected to replace conventional subtractive manufacturing technologies to some extents. During a selective laser melting (SLM) process as one of popular AM technologies for metals, large amount of heats is required to melt metal powders, and this leads to distortions and/or shrinkages of additively manufactured parts. It is useful to predict the 3D printed parts to control unwanted distortions and shrinkages before their 3D printing. This study develops a two-phase numerical modelling and simulation process of AM process for 17-4PH stainless steel and it considers the importance of post-processing and the need for calibration to achieve a high-quality printing at the end. By using this proposed AM modelling and simulation process, optimal process parameters, material properties, and topology can be obtained to ensure a part 3D printed successfully

The Behaviour of Cement Stabilized Clay At High Water Contents

Artificial cementation of soft clays has been used for several years for different ground improvement projects. Although considerable work has been done to develop advanced machinery and techniques for the implementation of artificial cementation, less knowledge is available on the mechanisms involving the formation of the artificial structure and the resulting mechanical behaviour. The primary objectives of the present work were to investigate the formation of microstructure in artificially cemented material with Portland cement, find the relationships between cementitious bonding and clay mineralogy, and create constitutive frameworks for predicting the mechanical behaviour of cement-treated clays. Qualitative and quantitative microstructural characterisation of reconstituted and cemented material has been performed using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results confirmed the transformation of the void microstructure from a bimodal, dispersed material into a unimodal, flocculated material due to artificial cementation. The addition of cement was found to reduce the amount of macro-pores within the cemented material, resulting in a significant reduction in hydraulic conductivity. A further parametric study was conducted on data obtained in the laboratory by the author combined with those found in the literature, to investigate the effect of clay mineralogy on artificial cementation. The results indicated the major influence of the activity of the clay, along with the cement and water content, on the results of the cement treatment. The observed variations in the mechanical behaviour with respect to mineralogy and the important effect of curing time have been explained in terms of the pozzolanic reactions, and the limitations of applying Abrams’ law to cement-admixed clays are discussed. In addition, an experimental study has been conducted to investigate the yielding and stress-strain behaviour of artificially cemented Ottawa clay and to compare it with the behaviour of the same soil in its naturally structured state. The results indicate that although the natural clay exhibits a meta-stable structure, resulting in an abrupt post-yield loss of strength, the artificially cemented material undergoes a more gradual breakage of the cementitious bonds. This allows for the use of the critical state concept, along with a pseudo-normal compression line, to develop a constitutive model for the artificially cemented material