Recycled glass as a supplementary filler material in spent coffee grounds geopolymers

Recycled glass (RG) is a demolition waste, rich in silica and with a high shear strength and has been used as a replacement material for sand in various construction applications. Spent coffee grounds (CG) is a waste material derived from brewing coffee and has been recently studied as a recycled construction material, due to its physical resemblance to sandy soils. Geopolymerization, is a green process which produces cementitious compounds using aluminosilicate-rich materials and alkaline liquids. In this research, a new geopolymer construction material was produced using RG as a supplementary filler material to stabilize CG. Fly ash (FA) and slag were used as the precursors to induce geopolymerization in this new RG + CG construction product. To maximize the potential strength of the geopolymer, fine RG was added into geopolymer mixes in proportions of 25%, 50%, and 75% to observe the effects on the final RG + CG product strength. The mixes were compressed into cylindrical specimens, cured at room temperature (i.e., 21 °C) and 50 °C for 7 and 28 days, and tested for their unconfined compressive strength (UCS) to observe the effect of the various RG replacement ratio on the strength of CG geopolymers. Scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS) were used to further explain the role of RG in influencing strength development. Higher RG contents were found to lead to higher UCS values. A lower liquid-to-precursor (L/P) ratio was required to achieve a saturation point in strength development. RG was found to provide mechanical strength and supplementary chemical bonding strengths by dissolving and contributing Si + ions to form geopolymeric substances

Laboratory approach for faster determination of the loading-collapse yield curve of compacted soils

A shift in the preconsolidation pressure or yield limit with suction, referred to as the loading-collapse (LC) yield curve, is an important feature of elastoplastic models of unsaturated soils. The LC curve is typically defined in the matric suction versus mean stress plane to account for the effects of matric suction. Conventional methods to determine the LC yield curve rely on a series of isotropic compression tests on specimens with identical stress history. This paper presents an alternative method to determine the LC yield curve from isotropic compression test results of specimens without identical stress history restrictions. A series of equations is proposed, derived from elastoplastic theory and incorporated into conventional compression test results, for drawing the specific LC yield curve. The advantage of the proposed methodology is that the compression tests results need not be taken from identical stress history specimens, which leads to a shorter time frame in the laboratory. Moreover, no additional parameters are required apart from those required in the conventional method. Test results from the literature are used to verify the proposed methodology, and a good agreement between the measured and calculated LC curves was found. The proposed methodology is a less time-consuming and more economical method to draw LC yield curve than the conventional method

Modeling the behavior of artificially structured clays by the Modified Structured Cam Clay model

Apractical constitutive model for artificially structured clays is formulated within the Structured Cam Clay (SCC) model framework, referred to as Modified Structured Cam Clay (MSCC) model. Based on experimental observation, it is considered that the effect of cementation is as the increase in mean effective stress. The strain softening behavior after the peak strength state caused by dilation and crushing of cementation structure for both normally and over-consolidated states can be simulated by the reduction in effective stressand the shrinkage of yield surface. The model parameters can be divided into those describing destructured properties and those for cementation structure, which can be simply determined from the conventional triaxial tests on artificially structured samples. The capability of the model is illustrated by the comparison of the simulated and measured undrained and drained shear responses of artificially structured Ariake clay

A study of the compression behaviour of structured clays

The compression behaviour of soils has always been a topic of investigation in geotechnical engineering. A study of the compression behaviour of soils with natural structures and with artificially treated structures is made in this paper. The voids ratio of any structured soil is the summation of the voids ratio of the same soil in a reconstituted state and the additional voids ratio sustained by the soil structure. This finding provides a useful framework for development of a compression model quantifying the influence of soil structures. Based on this model, a comparative study is performed on the influence of different types of soil structures on the compression behaviour. Therefore, the compressibility is investigated and quantified of soils in different states, such as reconstituted state, natural state, and chemical treated states and cemented state

Far Eastern survey

Columnar inclusion is one of the effective and widely used methods for improving engineering properties of soft clay ground. This paper investigates the consolidation behavior of composite soft clay ground using both physical model tests under an axial-symmetry condition and finite element simulations using the PLAXIS 2D program. Because the soil-cement column enhances the yield stress and stiffness of the composite ground, the composite ground is in an over-consolidated state under the applied vertical applied stresses. At this state, the rate of consolidation is rapid due to a high coefficient of consolidation. The consolidation of the composite ground is mainly controlled by the area ratio, the ratio of the diameter of the soil-cement column to the diameter of the composite ground, a . As the area ratio increases, the rate of consolidation increases and the final settlement decreases

Recycled glass as a supplementary filler material in spent coffee grounds geopolymers

Recycled glass (RG) is a demolition waste, rich in silica and with a high shear strength and has been used as a replacement material for sand in various construction applications. Spent coffee grounds (CG) is a waste material derived from brewing coffee and has been recently studied as a recycled construction material, due to its physical resemblance to sandy soils. Geopolymerization, is a green process which produces cementitious compounds using aluminosilicate-rich materials and alkaline liquids. In this research, a new geopolymer construction material was produced using RG as a supplementary filler material to stabilize CG. Fly ash (FA) and slag were used as the precursors to induce geopolymerization in this new RG + CG construction product. To maximize the potential strength of the geopolymer, fine RG was added into geopolymer mixes in proportions of 25%, 50%, and 75% to observe the effects on the final RG + CG product strength. The mixes were compressed into cylindrical specimens, cured at room temperature (i.e., 21 °C) and 50 °C for 7 and 28 days, and tested for their unconfined compressive strength (UCS) to observe the effect of the various RG replacement ratio on the strength of CG geopolymers. Scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS) were used to further explain the role of RG in influencing strength development. Higher RG contents were found to lead to higher UCS values. A lower liquid-to-precursor (L/P) ratio was required to achieve a saturation point in strength development. RG was found to provide mechanical strength and supplementary chemical bonding strengths by dissolving and contributing Si + ions to form geopolymeric substances

Cement stabilisation of recycled concrete aggregate modified with polyvinyl alcohol

During the past few decades, the engineering and geotechnical properties of recycled concrete aggregate (RCA) has been investigated to evaluate its potential to use as a road construction material. This research studied the usage of polyvinyl alcohol (PVA) and cement for improving the mechanical strengths of RCA to be used as an alternative material in pavement base/subbase applications. The results showed that mixing PVA > 1.5% into the cement-stabilised RCA has a vital role in improving the compressive strength along with gaining a higher modulus of toughness. The unconfined compressive strength (UCS) value of stabilised RCA with 3% cement and RCA with 3% cement and 1.5% or 2% PVA met the minimum requirement for 7 days of curing. The addition of PVA reduced the resilient modulus (MR); however, the MR value of all blends was still higher than the minimum recommended value. The specimens with 28 days of curing had higher resilient modulus values than 7-day cured samples. The CBR value and swelling in soaked condition reduced with increasing the PVA content. The cement-PVA-stabilised RCA, as a supplementary material with up to 1.5% or 2% PVA content and 3% General Portland (GP) were found to have physical and strength properties, which comply with road authority requirements