Using Artificial Neural Networks Approach to Estimate Compressive Strength for Rubberized Concrete

Artificial neural network (ANN) is a soft computing technique that has been used to predict with accuracy compressive strength known for its high variability of values. ANN is used to develop a model that can predict compressive strength of rubberized concrete where natural aggregate such as fine and coarse aggregate are replaced by crumb rubber and tire chips. The main idea in this study is to build a model using ANN with three parameters that are: water/cement ratio, Superplasticizer, granular squeleton. Furthermore, the data used in the model has been taken from various literatures and are arranged in a format of three input parameters: water/cement ratio, superplasticizer, granular squeleton that gathers fine aggregates, coarse aggregates, crumb rubber, tire chips and output parameter which is compressive strength. The performance of the model has been judged by using correlation coefficient, mean square error, mean absolute error and adopted as the comparative measures against the experimental results obtained from literature. The results indicate that artificial neural network has the ability to predict compressive strength of rubberized concrete with an acceptable degree of accuracy using new parameters

Humanitarian interventions and reasons for the lost opportunity to intervene in the Genocide of Rwanda in 1994

Contents: Traditional Peacekeeping to the new generation of peace-keeping operations; Internal conflicts and new threats; Approaches to humanitarian intervention and the dilemma of sovereignty; The failure of the humanitarian intervention in Rwanda; Conclusion

Birth Outcome and Maternal Risk Factors Associated with Childhood Leukemia in Rwanda: A case - Control Study

BackgroundLeukemia is the most common cancer affecting children and remains the top cause of death among children.ObjectiveThis study aimed at determining birth outcomes and maternal risk factors associated with childhood leukemia in Rwanda.MethodsA case control study was conducted at Butaro Cancer Referral hospital. The sample of 103 cases and 103 controls was recruited using the records for children diagnosed with Acute lymphocytic leukemia (ALL) and Acute myelogenous leukemia (AML) and those who were hospitalized for non-cancer treatment as controls. Semi-structured questionnaire and phone calls were used to gather information. SPSS version 21.0 was used to analyze the data. Logistic regression analysis was used to assess the risk factors.ResultsThe majority (56.8%) of children who participated in the study were aged 10-14 years. Overall 41.3% were born via C-Section. It was revealed that children who had had birth asphyxia had about three (3) times increased risk of childhood leukemia [AoR= 2.47, 95%CI: 1.167-5.262, P=0.018] compared to children that had not experienced birth asphyxia. Children who had suffered Neonatal Jaundice, had five (5) times increased risk of getting leukemia [AOR= 5.05, 95%CI: 1.738-14.664, P=0.003].ConclusionIt is important that public and private stakeholders invest more in childhood oncology researches to enable the health system deliver effective management of the cases more efficiently. Rwanda J Med Health Sci 2022;5(2):158-16

Utilization of Shredded Rubber Tires for Cement-Stabilized Soft Clays

Tire-soil mixtures can be used as good construction materials in many geotechnical engineering applications such as pavement foundations, lightweight fill in road embankments and lightweight backfill behind retaining walls. This paper describes research undertaken to investigate experimentally the impact of shredded rubber tires as reinforcing material on the mechanical properties of cement-stabilized soft clay, in terms of strength and stiffness. A series of laboratory experiments are carried out on cement-stabilized clay mixed with several portions of shredded rubber tires of sizes 440 m and 4 mm. The tests conducted include compaction, unconfmed compression strength and indirect tensile strength. The results demonstrate that the use of shredded rubber tires has a potential in enhancing the ductility of cement-stabilized soft clay but decreases stiffness and ultimate resistance

On the Fresh/Hardened Properties of Cement Composites Incorporating Rubber Particles from Recycled Tires

This study investigates the ameliorative effects on some properties of cement-based materials which can be obtained by incorporating rubber particles as part of the fine aggregates. The aim is to find out optimal cement composite/mortar mixtures, containing recycled-tyre rubber particles, suitable for specific engineering applications. Different percentages of rubber particles, from 0% to 75%, were used and, for each percentage, the suitable amount of sand was investigated in order to achieve the best fresh/hardened performances. In particular the following characteristics were examined: density, compressive strength, modulus of elasticity, shrinkage, weight loss, flexural behaviour, thermal conductivity, rapid freezing and thawing durability, and chloride permeability. The experimental results were compared with the ones of cement composite specimens without rubber aggregates. Test results show that the proposed rubberized mortar mixes are particularly suitable for some industrial and architectural applications, such as under-rail bearings, road constructions, paving slabs, false facades, and stone backing

Flexural characteristics of rubberized cement-stabilized crushed aggregate for pavement structure

The purpose of this paper is to investigate the flexural characteristics and to quantitatively study the flexural-induced cracking of reference and rubberized cement stabilized aggregate mixtures. Four volumetric replacement percentages (0%, 15%, 30% and 45%) of 6 mm fraction size were used. This modification was found to affect the material strength detrimentally. However, material toughness was improved and stiffness was reduced. The latter findings were supported by quantitative assessment of the fractured surfaces which revealed more tortuous and rougher cracking as a result of rubber content increasing. This, in turn, may ensure a good load transfer across the cracks after their formation. Overall, using rubber in pavement construction is a sustainable solution that ensures consumption of large quantities of these waste materials. At the same time, it may be considered as a promising method to reduce cracking tendency and sensitivity which may improve shrinkage, thermal and fatigue performance

Brittle Creep Failure, Critical Behavior, and Time-to-Failure Prediction of Concrete under Uniaxial Compression

Understanding the time-dependent brittle deformation behavior of concrete as a main building material is fundamental for the lifetime prediction and engineering design. Herein, we present the experimental measures of brittle creep failure, critical behavior, and the dependence of time-to-failure, on the secondary creep rate of concrete under sustained uniaxial compression. A complete evolution process of creep failure is achieved. Three typical creep stages are observed, including the primary (decelerating), secondary (steady state creep regime), and tertiary creep (accelerating creep) stages. The time-to-failure shows sample-specificity although all samples exhibit a similar creep process. All specimens exhibit a critical power-law behavior with an exponent of −0.51 ± 0.06, approximately equal to the theoretical value of −1/2. All samples have a long-term secondary stage characterized by a constant strain rate that dominates the lifetime of a sample. The average creep rate expressed by the total creep strain over the lifetime (tf-t0) for each specimen shows a power-law dependence on the secondary creep rate with an exponent of −1. This could provide a clue to the prediction of the time-to-failure of concrete, based on the monitoring of the creep behavior at the steady stage

Effect of Modified Rubber Particles Mixing Amount on Properties of Cement Mortar

The crumb rubber cement mortar is prepared by the crumb rubber aggregates in 60 mesh which are modified by 1% polyvinyl alcohol (PVA) solution. Some mechanical properties of cement mortar with different crumb rubber aggregate amounts are researched including compressive strength, flexural strength, the ratio of compressive strength to flexural strength, impact resistance, and dry contraction percentage. In our tests, we consider six kinds of the rubber contents, 0%, 7.5%, 15%, 19%, 22.5%, and 30%, respectively. The optimal mixing amount of crumb rubber is determined by measuring three indices, the ratio of compressive strength to flexural strength, impact resistance, and dry contraction percentage. It is shown by test that the ratio of compressive strength to flexural strength is the smallest when the mixing amount of rubber is 19%; meanwhile high impact resistance and rational drying shrinkage are observed. The optimal mixing amount of the rubber particles is 19% determined by this test

Influence du séchage sur le développement des hétérogénéités dans les structures à base de matériaux cimentaires : Impact sur les propriétés mécaniques

Ce travail décrit l’ensemble des phénomènes qui gouvernent le développement des hétérogénéités dans les structures à base de matériaux cimentaires lorsqu’elles sont soumises au séchage ainsi que leur influence sur les propriétés mécaniques du matériau mis en oeuvre. Il s’agit notamment des facteurs influents tels que la porosité, la teneur en humidité, le degré d’hydratation. Tous ces facteurs contribuent à la tenue du matériau in situ ainsi que son comportement au regard de la  fissuration. Il a été démontré pour ces matériaux que, les fissures s’amorcent dans la partie du matériau qui présente les propriétés les plus médiocres et qu’elles se propagent par la suite dans le reste du volume. Dans cette étude, nous nous sommes intéressés à la caractérisation et la quantification des gradients de propriétés tels que les gradients hydriques, les gradients d’hydratation et les gradients de porosités. Pour finir nous avons étudié leur impact sur l’évolution des propriétés mécaniques des matériaux mis en oeuvre. L’étude a révélé une parfaite adéquation entre la progression du front de séchage et les différentes hétérogénéités observées en terme de caractéristiques mécaniques.Mots-clés : matériaux cimentaires, béton, mortier, séchage, hétérogénéités, propriétés mécaniques

Optimisation of rubberised concrete with high rubber content: an experimental investigation

This article investigates experimentally the behaviour of rubberised concrete (RuC) with high rubber content so as to fully utilise the mechanical properties of vulcanised rubber. The fresh properties and short-term uniaxial compressive strength of 40 rubberised concrete mixes were assessed. The parameters examined included the volume (0–100%) and type of mineral aggregate replacement (fine or coarse), water or admixture contents, type of binder, rubber particle properties, and rubber surface pre-treatments. Microstructural analysis using a Scanning Electron Microscope (SEM) was used to investigate bond between rubber and concrete at the Interface Transition Zone (ITZ). This initial study led to the development of an “optimum” RuC mix, comprising mix parameters leading to the highest workability and strength at all rubber contents. Compared to a non-optimised concrete with 100% replacement of fine aggregates with rubber, the compressive strength of concrete with optimised binder material and moderate water/binder ratio was enhanced by up to 160% and the workability was improved significantly. The optimisation proposed in this study will lead to workable high rubber content RuC suitable for sustainable high-value applications