Construction and Demolition Waste Characteristics in Tanzania

The construction industry generates a lot of construction and demolition (C&D) waste which puts some challenges to its management. For example, currently, in many towns in Tanzania, there are no landfill sites for solid waste disposal; and as a consequence open air dumping sites are used. Dumping C&D waste puts pressure for acquisition of large portions of land in order to accommodate the disposal of the growing waste generated from construction and demolition sites. Others include imposed economic burdens, social discomfort as well as sources of environmental pollution like air and water pollutants. Due to population growth and land limitation for waste disposal, the current practices will put extra pressure on C&D waste management in future as well. This paper aims to investigate the quantity and quality of C&D waste in Tanzania and the possibilities for reusing and recycling this waste in the production of building materials. The use of C&D waste for building material production can be a best option not only for waste management but also for providing alternative building material for present and future generations. Materials used in this study were cementitious rubble recovered from eight building construction and demolition sites in Dar es Salaam. Two samples from natural sources were used for comparison purposes. Secondary data from Dar es Salaam City Council was used to estimate the amount of C&D waste generated in Tanzania annually. Furthermore, the recovered C&D waste samples were crushed to get recycled aggregates that were used in laboratory analysis. The results showed that the C&D waste generation in Tanzania increased from 3.03 million tonnes to 7.9 million tonnes in the period ranging from 1994 to 2010 years. Furthermore, the results showed that the recycled aggregates were weaker than natural aggregates, however, mineralogically were not significantly different from natural aggregates. Thus, their chemical composition similarities suggest that recycled C&D waste is suitable for production of building materials in Tanzania. The recycling of C&D waste into building material will contribute to sustainable social, economic, and environmental improvements

Pediatric Differentiated Thyroid Carcinoma in The Netherlands: A Nationwide Follow-Up Study

Introduction: Treatment for differentiated thyroid carcinoma (DTC) in pediatric patients is based mainly on evidence from adult series due to lack of data from pediatric cohorts. Our objective was to evaluate presentation, treatment-related complications, and long-term outcome in patients with pediatric DTC in the Netherlands. Patients and methods: In this nationwide study, presentation, complications and outcome of patients with pediatric DTC (age at diagnosis ≤18 years) treated in the Netherlands between 1970 and 2013 were assessed using medical records. Results: We identified 170 patients. Overall survival was 99.4% after median follow-up of 13.5 (range 0.3–44.7) years. Extensive follow-up data were available for 105 patients (83.8% women), treated in 39 hospitals. Median age at diagnosis was 15.6 (range 5.8–18.9) years. At initial diagnosis, 43.8% of the patients had cervical lymph node metastases; 13.3% had distant metastases. All patients underwent total thyroidectomy. Radioiodine was administered to 97.1%, with a median cumulative activity of 5.66 (range 0.74–35.15) GBq. Lifelong postoperative complications (permanent hypoparathyroidism and/or recurrent laryngeal nerve injury) were present in 32.4% of the patients. At last known follow-up, 8.6% of the patients had persistent disease and 7.6% experienced a recurrence. TSH suppression was not associated with recurrences (OR 2.00, 95% CI 0.78 to 5.17, P = 0.152). Conclusions: Survival of pediatric DTC is excellent. Therefore, minimizing treatment-related morbidity takes major priority. Our study shows a frequent occurrence of lifelong postoperative complications. Adverse effects may be reduced by centralization of care, which is crucial for children with DTC

A hydration model of Portland cement using the work of Powers and Brownyard

This book addresses the hydration of ordinary portland cement, the principal hydraulic binder used in building and civil engineering. More specifically the composition of the cement paste as well as the individual chemical reactions of the four major clinker phases and calcium sulfates with water are dealt with. The water needed for the hydration, and the type and quantity of hydration products formed are discussed in detail. The underlying information on chemical shrinkage and water binding is taken from the classic work by Powers and Brownyard (1948). Fundamental properties, such as the chemical and microstructural aspects are discussed. The emphasis throughout is on understanding the composition of cement paste and relating it to the composition of the cement and the water binder ratio involved

Packing fraction of particles with a Weibull size distribution

\u3cp\u3eThis paper addresses the void fraction of polydisperse particles with a Weibull (or Rosin-Rammler) size distribution. It is demonstrated that the governing parameters of this distribution can be uniquely related to those of the lognormal distribution. Hence, an existing closed-form expression that predicts the void fraction of particles with a lognormal size distribution can be transformed into an expression for Weibull distributions. Both expressions contain the contraction coefficient β. Likewise the monosized void fraction φ1, it is a physical parameter which depends on the particles' shape and their state of compaction only. Based on a consideration of the scaled binary void contraction, a linear relation for (1-φ1)β as function of φ1 is proposed, with proportionality constant B, depending on the state of compaction only. This is validated using computational and experimental packing data concerning random close and random loose packing arrangements. Finally, using this β, the closed-form analytical expression governing the void fraction of Weibull distributions is thoroughly compared with empirical data reported in the literature, and good agreement is found. Furthermore, the present analysis yields an algebraic equation relating the void fraction of monosized particles at different compaction states. This expression appears to be in good agreement with a broad collection of random close and random loose packing data.\u3c/p\u3

Viscosity of a concentrated suspension of rigid monosized particles

\u3cp\u3eThis paper addresses the relative viscosity of concentrated suspensions loaded with unimodal hard particles. So far, exact equations have only been put forward in the dilute limit, e.g., by Einstein for spheres. For larger concentrations, a number of phenomenological models for the relative viscosity was presented, which depend on particle concentration only. Here, an original and exact closed form expression is derived based on geometrical considerations that predicts the viscosity of a concentrated suspension of monosized particles. This master curve for the suspension viscosity is governed by the relative viscosity-concentration gradient in the dilute limit (for spheres the Einstein limit) and by random close packing of the unimodal particles in the concentrated limit. The analytical expression of the relative viscosity is thoroughly compared with experiments and simulations reported in the literature, concerning both dilute and concentrated suspensions of spheres, and good agreement is found.\u3c/p\u3

Packing of crystalline structures of binary hard spheres: an analytical approach and application to amorphisation

The geometrical stability of the three lattices of the cubic crystal system, viz. face-centered cubic (fcc), body-centered cubic (bcc), and simple cubic (sc), consisting of bimodal discrete hard spheres, and the transition to amorphous packing is studied. First, the random close packing (rcp) fraction of binary mixtures of amorphously packed spheres is recapitulated. Next, the packing of a binary mixture of hard spheres in randomly disordered cubic structures is analyzed, resulting in original analytical expressions for the unit cell volume and the packing fraction, and which are also valid for the other five crystal systems. The bimodal fcc lattice parameter appears to be in close agreement with empirical hard sphere data from literature, and this parameter could be used to distinguish the size mismatch effect from all other effects in distorted binary lattices of materials. Here, as a first model application, bimodal amorphous and crystalline fcc/bcc packing fractions are combined, yielding the optimum packing configuration, which depends on mixture composition and diameter ratio only. Maps of the closest packing mode are established and applied to colloidal mixtures of polydisperse spheres and to binary alloys of bcc, fcc, and hcp metals. The extensive comparison between the analytical expressions derived here and the published numerical and empirical data yields good agreement. Hence, it is seen that basic space-filling theories on simple noninteracting hard spheres are a valuable tool for the study of crystalline materials

Packing fraction of particles with a lognormal size distribution

This paper addresses the packing and void fraction of polydisperse particles with a lognormal size distribution. It is demonstrated that a binomial particle size distribution can be transformed into a continuous particle-size distribution of the lognormal type. Furthermore, an original and exact expression is derived that predicts the packing fraction of mixtures of particles with a lognormal distribution, which is governed by the standard deviation, mode of packing, and particle shape only. For a number of particle shapes and their packing modes (close, loose) the applicable values are given. This closed-form analytical expression governing the packing fraction is thoroughly compared with empirical and computational data reported in the literature, and good agreement is found