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Papers by Khosrow Ghavami

Key Engineering Materials, Oct 1, 2015

The use of compressed earth blocks (CEBs) is widespread in the field of earth construction. They ... more The use of compressed earth blocks (CEBs) is widespread in the field of earth construction. They present better mechanical performance than adobe and the equipment for their production is simple. Laboratory testing of compressed earth blocks requires large amounts of material. There are variations of unconfined strength testing procedures such as testing halves of the blocks with layers of mortar between them or testing whole blocks in diverse directions. This complicates the interpretation of test results as the shape factor and mortar characteristics influence the results significantly. Static compaction test can be used to produce cylindrical samples representative of CEBs. The water content of soil used for the production of CEBs is often determined in standard Proctor test while experimental data indicate that the optimum moisture content for static and dynamic compaction is different. The present article addresses the behavior of four soil mixes with varying clay content compacted statically with a constant rate of strain. Static compaction curves were compared with those obtained in standard Proctor test. For all the soil mixes the static optimum moisture content was found to correspond to the start of consolidation. The compaction curve presented no wet side of optimum in contrast to Proctor test. The energy needed to achieve a desired density by static compaction was analyzed for soils with varying clay contents. Static compaction was found to be more efficient than dynamic for clayey soils. An increase in water content was observed to help achieving higher densities at low pressures, which can improve the performance of manual CEB presses.

ACI Materials Journal, 2008

ABSTRACT Sugar cane bagasse ash (SCBA) is generated as a combustion by-product from boilers of su... more ABSTRACT Sugar cane bagasse ash (SCBA) is generated as a combustion by-product from boilers of sugar and alcohol factories. Composed mainly of silica, this by-product can be used as a mineral admixture in concrete. In this investigation, conventional and high-performance concretes (CCs and HPCs, respectively) were produced with 0, 10, 15, and 20% of a residual ultra-fine SCBA as cement replacement (in mass). For these concretes, rheological, mechanical, durability, and adiabatic calorimetric tests were performed. The results indicate that the mechanical properties of concretes were not significantly changed by the use of SCBA for all levels of replacement. The ultra-fine SCBA concretes presented superior performance in the rheological, water sorption capillary, and rapid chloride-ion permeability tests as compared with the reference mixture. The maximum adiabatic temperature rise of CC substantially decreased (11%) by replacement of 15% of cement by ultra-fine SCBA.

Revista Digital del Cedex, Apr 1, 2003

ACI Materials Journal, 1998

Materials Research-ibero-american Journal of Materials, Jun 7, 2013

Elsevier eBooks, 2009

Cellulosic-pulp-reinforced cement sheets are produced in large scale for more than 25 years. This... more Cellulosic-pulp-reinforced cement sheets are produced in large scale for more than 25 years. This followed studies that had focused on the fibre and matrix characteristics, and on their composite behaviour, solving to a limited extent the problems arising from fibre-matrix incompatibility and deterioration due to alkali attack. In spite of that, much has yet to be done in terms of providing a material with properties competitive with those of asbestos cement, mainly considering their long term performances. Current research on cellulose-pulp reinforced cement composites concentrates on evaluating the deterioration mechanisms, the treatment methods and the modelling of the effects of these mechanisms on the physical, mechanical and micro-structural aspects of the material. Interfacial adhesion governs the mechanical behaviour and many physical properties of composites. Therefore, it is a key issue when focusing on durability, since the deterioration mechanisms and the treatment methods exert direct influences on the fibre-matrix interface. Direct assessment of adhesion strength by pull-out tests on fibres generally shorter than 2 mm in cellulose-cement composites presents practical difficulties. Also, direct application of the equations derived from the composite's micromechanics to this type of cement composites, as produced by the vacuum-dewatering process, and containing high volume fractions of curly fibres would be problematic. Fortunately, a significant amount of data is available in the literature regarding the physical and mechanical behaviour of cellulose-cement composites of a variety of compositions and produced under similar conditions. This allows establishing mutual correlations. This is used as reference framework for the design of the cellulose-cement compositions tested by the authors. The outcomes reveal this approach a valuable tool in comparative studies on the mechanical behaviour of cellulose-cement composites dealing with effects of treatment methods, deterioration mechanisms and processing parameters.

Journal of building engineering, Nov 1, 2021

More recent investigations on cellulose-cement composites predominantly deal with durability aspe... more More recent investigations on cellulose-cement composites predominantly deal with durability aspects, whereby use is made of accelerated weathering cycles as the main approach to establishing the deterioration mechanisms and the efficiency of treatment methods. As moisture transport is the main mechanism that leads to the deterioration of those composites, accelerated ageing tests are commonly based on wet-drying cycles with a combination of temperature and relative humidity (R.H.) variations. Both variables result in dimensional changes of the samples, leading to interfacial abrasion and the progressive decrease in the composites’ toughness and strength. To investigate the effects of each of these variables, the weathering tests were performed in an environmental chamber considering each variable separately in two ageing cycles. In the first one the composites were submitted to saturation and drying at a constant 25 °C, by means of a relative humidity change in the chamber. For the second ageing cycle a temperature variation between 20 °C and 60 °C at a constant R.H. of 50% was applied. The effects of each ageing cycle on the cellulose-cement composites were assessed on the basis of physical and mechanical parameters, determined after 0, 5, 20 and 50 cycles. Moreover, part of the samples was provided with electrical strain gauges, which rendered possible to determine the composites’ expansion-shrinkage behaviour during the temperature and R.H. variations. As the main treatment approach, the partial replacement of cement (OPC) by rice husk ash (RHA) was investigated. It was found that RHA improved the strength and durability performance of the composites, although the increased porosity resulted from the 30% replacement rate of OPC and carbonate filler by RHA.

Industrial Crops and Products, Dec 1, 2015

Construction and Building Materials, Oct 1, 2018

Journal of Materials Science, Nov 1, 2006

... the basis of capillary and gel pores, by combining these two phases through an effective medi... more ... the basis of capillary and gel pores, by combining these two phases through an effective media theory, was developed by Cui and Cahyadi [26]. ... were grounded in a ceramic ball mill for 12 h. Table 1 presents data on the chemical composition, pozzolanic index ∆mS/cm, specific ...

Revista Brasileira de Engenharia Agricola e Ambiental, Dec 1, 1997

Journal- International Association for Shell and Spatial Structures, Sep 30, 2016

Proceedings of the Institution of Civil Engineers, Apr 1, 2017

Guadua angustifolia is a species of bamboo exhibiting excellent mechanical properties in the axia... more Guadua angustifolia is a species of bamboo exhibiting excellent mechanical properties in the axial direction, which have been extensively investigated. Few studies have measured other anisotropic constants, which are necessary for reliable theoretical analyses. A simple new protocol is proposed to determine the circumferential–axial shear modulus and axial Young's modulus of this bamboo species by loading slats under torsion and bending. Different theoretical formulations were considered to correlate with the experimental data. The circumferential–axial shear modulus was determined using a torsion formula of strength of materials and an orthotropic finite-element model. The axial Young's modulus obtained using the strength of materials formula was higher than those determined using finite-element orthotropic, isotropic and functionally graded models. The shear and axial moduli obtained with the strength of materials formulae provided relatively good estimates of beam deflections. This protocol can be applied to assess the mechanical properties of other species of bamboo and wood used in structural engineering practice.

Waste and Biomass Valorization, Apr 13, 2010

Key Engineering Materials, Oct 1, 2015

The use of compressed earth blocks (CEBs) is widespread in the field of earth construction. They ... more The use of compressed earth blocks (CEBs) is widespread in the field of earth construction. They present better mechanical performance than adobe and the equipment for their production is simple. Laboratory testing of compressed earth blocks requires large amounts of material. There are variations of unconfined strength testing procedures such as testing halves of the blocks with layers of mortar between them or testing whole blocks in diverse directions. This complicates the interpretation of test results as the shape factor and mortar characteristics influence the results significantly. Static compaction test can be used to produce cylindrical samples representative of CEBs. The water content of soil used for the production of CEBs is often determined in standard Proctor test while experimental data indicate that the optimum moisture content for static and dynamic compaction is different. The present article addresses the behavior of four soil mixes with varying clay content compacted statically with a constant rate of strain. Static compaction curves were compared with those obtained in standard Proctor test. For all the soil mixes the static optimum moisture content was found to correspond to the start of consolidation. The compaction curve presented no wet side of optimum in contrast to Proctor test. The energy needed to achieve a desired density by static compaction was analyzed for soils with varying clay contents. Static compaction was found to be more efficient than dynamic for clayey soils. An increase in water content was observed to help achieving higher densities at low pressures, which can improve the performance of manual CEB presses.

ACI Materials Journal, 2008

ABSTRACT Sugar cane bagasse ash (SCBA) is generated as a combustion by-product from boilers of su... more ABSTRACT Sugar cane bagasse ash (SCBA) is generated as a combustion by-product from boilers of sugar and alcohol factories. Composed mainly of silica, this by-product can be used as a mineral admixture in concrete. In this investigation, conventional and high-performance concretes (CCs and HPCs, respectively) were produced with 0, 10, 15, and 20% of a residual ultra-fine SCBA as cement replacement (in mass). For these concretes, rheological, mechanical, durability, and adiabatic calorimetric tests were performed. The results indicate that the mechanical properties of concretes were not significantly changed by the use of SCBA for all levels of replacement. The ultra-fine SCBA concretes presented superior performance in the rheological, water sorption capillary, and rapid chloride-ion permeability tests as compared with the reference mixture. The maximum adiabatic temperature rise of CC substantially decreased (11%) by replacement of 15% of cement by ultra-fine SCBA.

Revista Digital del Cedex, Apr 1, 2003

ACI Materials Journal, 1998

Materials Research-ibero-american Journal of Materials, Jun 7, 2013

Elsevier eBooks, 2009

Cellulosic-pulp-reinforced cement sheets are produced in large scale for more than 25 years. This... more Cellulosic-pulp-reinforced cement sheets are produced in large scale for more than 25 years. This followed studies that had focused on the fibre and matrix characteristics, and on their composite behaviour, solving to a limited extent the problems arising from fibre-matrix incompatibility and deterioration due to alkali attack. In spite of that, much has yet to be done in terms of providing a material with properties competitive with those of asbestos cement, mainly considering their long term performances. Current research on cellulose-pulp reinforced cement composites concentrates on evaluating the deterioration mechanisms, the treatment methods and the modelling of the effects of these mechanisms on the physical, mechanical and micro-structural aspects of the material. Interfacial adhesion governs the mechanical behaviour and many physical properties of composites. Therefore, it is a key issue when focusing on durability, since the deterioration mechanisms and the treatment methods exert direct influences on the fibre-matrix interface. Direct assessment of adhesion strength by pull-out tests on fibres generally shorter than 2 mm in cellulose-cement composites presents practical difficulties. Also, direct application of the equations derived from the composite's micromechanics to this type of cement composites, as produced by the vacuum-dewatering process, and containing high volume fractions of curly fibres would be problematic. Fortunately, a significant amount of data is available in the literature regarding the physical and mechanical behaviour of cellulose-cement composites of a variety of compositions and produced under similar conditions. This allows establishing mutual correlations. This is used as reference framework for the design of the cellulose-cement compositions tested by the authors. The outcomes reveal this approach a valuable tool in comparative studies on the mechanical behaviour of cellulose-cement composites dealing with effects of treatment methods, deterioration mechanisms and processing parameters.

Journal of building engineering, Nov 1, 2021

More recent investigations on cellulose-cement composites predominantly deal with durability aspe... more More recent investigations on cellulose-cement composites predominantly deal with durability aspects, whereby use is made of accelerated weathering cycles as the main approach to establishing the deterioration mechanisms and the efficiency of treatment methods. As moisture transport is the main mechanism that leads to the deterioration of those composites, accelerated ageing tests are commonly based on wet-drying cycles with a combination of temperature and relative humidity (R.H.) variations. Both variables result in dimensional changes of the samples, leading to interfacial abrasion and the progressive decrease in the composites’ toughness and strength. To investigate the effects of each of these variables, the weathering tests were performed in an environmental chamber considering each variable separately in two ageing cycles. In the first one the composites were submitted to saturation and drying at a constant 25 °C, by means of a relative humidity change in the chamber. For the second ageing cycle a temperature variation between 20 °C and 60 °C at a constant R.H. of 50% was applied. The effects of each ageing cycle on the cellulose-cement composites were assessed on the basis of physical and mechanical parameters, determined after 0, 5, 20 and 50 cycles. Moreover, part of the samples was provided with electrical strain gauges, which rendered possible to determine the composites’ expansion-shrinkage behaviour during the temperature and R.H. variations. As the main treatment approach, the partial replacement of cement (OPC) by rice husk ash (RHA) was investigated. It was found that RHA improved the strength and durability performance of the composites, although the increased porosity resulted from the 30% replacement rate of OPC and carbonate filler by RHA.

Industrial Crops and Products, Dec 1, 2015

Construction and Building Materials, Oct 1, 2018

Journal of Materials Science, Nov 1, 2006

... the basis of capillary and gel pores, by combining these two phases through an effective medi... more ... the basis of capillary and gel pores, by combining these two phases through an effective media theory, was developed by Cui and Cahyadi [26]. ... were grounded in a ceramic ball mill for 12 h. Table 1 presents data on the chemical composition, pozzolanic index ∆mS/cm, specific ...

Revista Brasileira de Engenharia Agricola e Ambiental, Dec 1, 1997

Journal- International Association for Shell and Spatial Structures, Sep 30, 2016

Proceedings of the Institution of Civil Engineers, Apr 1, 2017

Guadua angustifolia is a species of bamboo exhibiting excellent mechanical properties in the axia... more Guadua angustifolia is a species of bamboo exhibiting excellent mechanical properties in the axial direction, which have been extensively investigated. Few studies have measured other anisotropic constants, which are necessary for reliable theoretical analyses. A simple new protocol is proposed to determine the circumferential–axial shear modulus and axial Young's modulus of this bamboo species by loading slats under torsion and bending. Different theoretical formulations were considered to correlate with the experimental data. The circumferential–axial shear modulus was determined using a torsion formula of strength of materials and an orthotropic finite-element model. The axial Young's modulus obtained using the strength of materials formula was higher than those determined using finite-element orthotropic, isotropic and functionally graded models. The shear and axial moduli obtained with the strength of materials formulae provided relatively good estimates of beam deflections. This protocol can be applied to assess the mechanical properties of other species of bamboo and wood used in structural engineering practice.

Waste and Biomass Valorization, Apr 13, 2010