Development of shrinkage resistant cement-based materials using fibers

Copyright © 2011 by Research Publishing Services. Drying shrinkage is themajor contributor to volume changes in normal strength concrete. Several classes of shrinkage compensating admixtures are known to the concrete industry. This study deals with the literature review and categorization of different classes of shrinkage reducing fibers, especially polyethylene fibers, with the objective of introducing new types of shrinkage reducing fiber. In this investigation a special type of hydrophobic polyethylene minifibers has been used in different dosages in mortar samples. The experimental results on drying shrinkage aswellasonseveralotherpropertiesarereported.Thehydrophobicminifibersshowedremarkable improvement in shrinkage reduction even at very lowconcentrations (0.1%of cementweight)

Evaluation of a hybrid system of admixture and fibre for development of shrinkage resistant cement-based material

Shrinkage is a crucial feature in concrete and mortar members as it results in volume change that can lead to cracking and consequently to serviceability problems. Different additives and methods have been proposed to compensate for this problem mainly through the use of shrinkage reducing admixtures, fibres and expansive agents. In this paper, several combination systems of polyethylene micro-fibre along with an inorganic expansive agent have been studied for their influence on drying shrinkage. This special type of fibre, reported to act as shrinkage reducer, had been used in different concentrations in mortars and had been shown to have advantages and disadvantages. On the other hand, expansive agent, ammonium polyphosphate, had been shown to reduce drying shrinkage and modify most of mechanical properties. Free shrinkage strains as well as some physical properties of new mixes which contain polyphosphate and polyethylene micro-fibre are reported in this study. Several combinations were used and have been shown to have promising results in drying shrinkage, physical and mechanical properties

A closed-loop system of construction and demolition waste recycling

This study discusses the construction and demolition waste recycling stream both in Australia and in Germany. Differences and commonalities in commercial practices between the two countries are outlined, and open research questions are introduced. Following McDonough and Braungart's cradle-to-cradle theorem, and ideal closed-loop system within the building life cycle is proposed. Deficiencies and efficiencies in the closed-loop system are reported and assessed and related parameters promoting or hindering the closed-loop system are evaluated. Results of the study demonstrate that reusable and non-reusable materials generated from construction and demolition operations, which are destined for landfill, are categorized differently between the recycling systems used in Australia and Germany

Development of shrinkage resistant microfibre-reinforced cement-based composites

© Versita sp. z o.o. Different shrinkage types may cause serious durability dilemma on restrained concrete parts due to crack formation and propagation. Several classes of fibres are used by concrete industry in order to reduce crack size and crack number. In previous studies, most of these fibre types were found to be effective in reducing the number and sizes of the cracks, but not in shrinkage strain reduction. This study deals with the influence of a newly introduced type of polyethylene fibre on drying shrinkage reduction. The novel fibre is a polyethylene microfibre in a new geometry, which is proved to reduce the amount of total shrinkage in mortars. This special hydrophobic polyethylene microfibre also reduces moisture loss of mortar samples. The experimental results on short and long-term drying shrinkage as well as on several other properties are reported. The hydrophobic polyethylene microfibre showed promising improvement in shrinkage reduction even at very low concentrations (0.1% of cement weight)

New mechanisms for drying shrinkage compensation in cementitious materials

There are several materials and methods which have been designed and used for reduction or compensation of drying shrinkage deformations in cementitious materials, in both industry and research . Typical strategies currently used in industry for overcoming drying shrinkage include introduction of expansive agents; use of shrinkage reducing admixtures (SRA) and fibres as components of mixtures; cement modification; and, taking advantage of internal curing (Kovler & Zhutovsky, 2006)

Implications of legal frameworks on construction and demolition waste recycling-A comparative study of the German and Australian systems

This comparative study between German and Australian legislation demonstrates that legal frameworks impact on the way in which recycling systems work. Both Australia and Germany operate as Federations and the autonomy of states influences common federation wide practices and standards. In Germany's case however, it is obliged to comply with European Union guidelines which result in German federal legislation being binding for all German states and to common industry practices across all of Germany. Purely industry regulated systems are not always sufficient to cater for societal and environmental needs, and political intervention can sometimes be necessary to achieve desired outcomes. The construction and demolition (C&D) waste recycling industry is a good example. In Australia C&D waste recycling is mostly industry regulated, while the state has greater influence in Germany. A statistical analysis illustrates legislative impact on recycling outcomes. Nonetheless, any legislative efforts can also have effects contrary to the intended ones. A study of such cases is conducted and other influencing factors also considered. In conclusion, the study outlines the importance of interstate coordination and regulation; and the need for the incorporation of industry requirements and other potentially influencing factors into the legal frameworks in order to meet desired outcomes

Structural response monitoring of concrete beam under flexural loading using smart carbon black/cement-based sensors

© 2020 IOP Publishing Ltd. The fractional changes of resistivity (FCR) of cement-based sensors with various carbon black (CB) contents were firstly investigated under uniaxial compression in this study. Then the piezoresistive behaviours of embedded cement-based sensors in unreinforced small-scale concrete beams were investigated under flexural bending load. As for the embedded cement-based sensors in the compression zones of the beam, the stress magnitude and crack failure initiation of the beams can be detected and monitored by a gradual decrease and then a sharp increase in the FRC. On the other hand, as for the counterpart sensors in the tension zones of the beam, the stress magnitude and crack failure initiation can be recognized by the gradual increase in resistivity and then a rapid jump in the FRC. During the stress monitoring of the concrete beam, the FCR values of cement-based sensors in both the compression and tension zones were consistent with the flexural stress changes, which exhibit acceptable sensitivity and reversibility. Moreover, very firm and dense interfaces in the boundaries indicate the excellent cohesion between embedded CB/cement-based sensors and beams. The related results demonstrate that the CB/cement-based sensors embedded in concrete exhibit excellent piezoresistive behaviours to potentially monitor the stress magnitude and failure process of concrete structures and pavements

A novel multi-functional expansive additive for drying shrinkage reduction in mortars

Several shrinkage compensating additives and admixtures are currently used in mortar and concrete. This study deals with the literature review and categorization of different classes of expansive additives with the objective of introducing a new range of polymeric additive. In this investigation an inorganic polymer, which is a multifunctional expansive additive, was used in different mixes of mortar. The results of experiments on drying shrinkage as well as its effect on several physical properties are reported. The new polymeric additive used in the experiments were found to decrease the amount of drying shrinkage when compared with a control mixture through the reaction of the inorganic polymer with calcium hydroxide forming a stable binder as well as an expansive agent. This new additive also proved to have a positive effect on some fresh and hardened properties of mortar. © 2011 Taylor & Francis Group, London

Trisomy 6 and double minute chromosomes in a case of chronic myelomonocytic leukemia

A 65-year-old woman with chronic myelomonocytic leukemia was shown to have trisomy 6 and multiple double minute chromosomes. The patient had no history of prior exposure to any mutagenic or carcinogenic agents. To our knowledge, this is the first report for presence of only these two aberrations. The expression of several oncoproteins and once-related proteins was detected immunohistochemically in bone marrow cells. Among them, only the bcl-2 oncoprotein was positively stained in 100% of myeloblasts. Although the c-myc oncogene is frequently reported to be overexpressed in myeloid disorders with double minutes and associated with chemotherapy resistance and disease aggressiveness, in our case, the c-myc oncoprotein was not positively expressed. The patient received chemotherapy and complete hematological remission rr as successfully achieved. (C) Elsevier Science Inc., 1998

Infectious complications following allogeneic stem cell transplantation by using anti-thymocyte globulin-based myeloablative conditioning regimens in children with hemoglobinopathies

Background: Anti-thymocyte globulin (ATG) has been used to prevent graft failure/rejection in the setting of allogeneic stem cell transplantation (allo-SCT) for hemoglobinopathies; however, epidemiology data for transplant-related infections in this population are scarce. Method: We retrospectively analyzed the epidemiology of bacterial, fungal, viral, and parasitic infections in a cohort of 105 children and adolescents with β-thalassemia (n = 100) or sickle cell disease (n = 5) who underwent allo-SCT using human leukocyte antigen (HLA)-identical sibling (n = 96) or HLA-compatible unrelated donors (n = 9) in a single institution. All patients received an ATG-based conditioning regimen. Results: The cumulative incidence of cytomegalovirus (CMV) viremia was 45.7% (95% confidence interval [CI] 33-55%), developing at a median of 48 (range 12-142) days without evidence of overt CMV disease. Herpes zoster developed in 8 patients at a median of 12 months post transplant, while 10 patients presented with late onset hemorrhagic cystitis at a median of 35 days post transplant. The cumulative incidence of bacteremia was 17.1% (95% CI 10.6-25%), occurring at a median of 74 (range 24-110) days. No patient developed probable or definite invasive fungal infection. Four deaths were recorded; 2 of them were attributed to infections (toxoplasmosis and Pneumocystis jirovecii pneumonia, respectively). Conclusion: The rate of infections after allo-SCT, using an ATG-containing preparative regimen, in our population of pediatric patients with hemoglobinopathies is comparable to that reported elsewhere with the use of non-ATG containing regimens. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd