ABSTRACT A large amount of discarded tire waste generated year after year has encouraged the scientific community to seek alternatives for recycling or reusing this waste. The cross-linked nature and the high number of additives in tires make recycling significantly difficult. Thus, the use of particulate rubber as filler for other materials such as concrete has emerged as an attractive alternative. However, the hydrophobic nature of the rubber and hydrophilic particles of cement decreases the compatibility at the cementitious matrix-rubber interface, affecting the concrete's final performance. This work presents a method based on hydrogen peroxide and Fenton for the oxidation of rubber particles from end-of-life tires to introduce hydrophilic groups on the surface of the particles to improve compatibility at the interface. The method was studied from an experimental design approach based on the infrared spectroscopy response and using a Rechtschaffner Resolution V design, PCA and PLSR in order to evaluate variables such as time, temperature and reactants. The concentration of H2O2 and reaction temperature was shown to increase the oxidation, while Fenton reduces the time of oxidation.

Abstract: Short slabs are a concrete pavement innovation that represents a change of paradigm in the traditional design (where the number of joints is limited). In this innovative approach, the concrete slab is designed in a way that no more than one set of vehicle wheels is actually on the slab. In this way, the stresses are reduced. The research related with this innovation has been focused in urban and interurban pavements, where the costs have been reduced even until 25%. On the other hand, the traffic demands over industrial floors are different from concrete pavements of streets or highways. In addition, the weather demands are different because a roof covers industrial floors. The objective of the present article is to analyze the stresses of short slabs for industrial floors using finite elements models in order to generate design recommendations. For that, a factorial design including variables as the pavement location, time of construction, slab geometry and traffic is defined. The results show that short slabs can generate significant costs reductions in certain industrial floors, but that they are not necessarily the best option for all the analyzed scenarios. However, short slabs are an attractive alternative for industrial floors commonly used as warehouses.

Resumen: Las losas cortas son una innovación en el área de pavimentos de hormigón, que implica un cambio de paradigma respecto al diseño, donde usualmente se limita el número de juntas. En este enfoque, el tamaño de la losa se diseña de tal manera que no más de un set de ruedas del vehículo quede sobre ella, con el objetivo de reducir las tensiones. La investigación asociada a esta innovación ha estado focalizada en pavimentos urbanos e interurbanos donde se han generado ahorros económicos de hasta un 25%. Por otra parte, los pisos industriales de hormigón tienen solicitaciones distintas a los caminos y carreteras, las cargas de tráfico son diferentes y los efectos climáticos considerados no son los mismos debido a que el piso industrial se encuentra, por lo general, cubierto por una estructura. El objetivo de este artículo es analizar el estado tensional de losas cortas bajo solicitaciones de pisos industriales mediante modelación de elementos finitos para generar recomendaciones de diseño. Esto se lleva a cabo mediante un análisis factorial que considera variables como localización del pavimento, fecha de construcción, geometría de las losas y tráfico. Los resultados indican que las losas cortas si pueden generar ahorros significativos en ciertos pisos industriales, pero que no son la mejor opción en todos los escenarios analizados. Sin embargo, son una muy atractiva alternativa para pisos industriales tipo bodega de uso masivo.

AbstractDuring the construction of Jointed Plain Concrete Pavements (JPCPs) in Chile, it was observed that joints remained uncracked. The objectives of this paper are to evaluate the effects of uncracked joints (UnCrJ) in JPCPs and to propose possible solutions or improvements to avoid or minimize this phenomenon. Considering low thermal amplitude as cause of UnCrJ, a rational-based, detailed and empirically validated model is used to predict UnCrJ and crack width. The modelled results are not only due to material changes but also to the location of the series of cracks in time in the JPCP system. The paper contributes with this rational approach, instead of an empirical-simplified one, to achieve the objectives. For the modelled conditions, the "as-built" slab length range is 8 m to 56 m instead of the 4 m designed one. Then, more curling, joint faulting, water infiltration in sealed joints and load transfer efficiency ≤ 70% are expected. The alternative solutions proposed are associated to innovations as short joints spacing, unsealed joints and saw-cuts up to 50% thickness made with thin blade (≤ 3mm), which was verified with new field evidence provided in the article.

Abstract Nowadays, there are Concrete Pavements (CPs) with Joints Configurations (JCs) that reduce initial costs about 20%. But are these JCs produced by Early-Entry Saw-Cutting (EESC), Unsealed Joints (UJs) and Shorter Joint Spacing (ShJS) able to maintain the traditional performance of CPs? The aim of this paper is to analyze the effects of the joints behaviour (JB) on the performance of CPs with these JCs. The JB is characterized by joints activation, opening, deterioration and Load Transfer Efficiency (LTE), not in an isolated but in a comprehensive way to determine not only the complete JB, but their effects on the CPs performance, so upon the users. The paper contributes not only with a comprehensive analysis of the innovative JCs, but also with new field experiences, that allow concluding the JCs can maintain or even improve the traditional performance of CPs if the saw-cutting depth ≥ 30% to assure 100% joints activation, joints opening < 1.2 mm, so LTE ≥ 70%. UJs with thin blade (< 3 mm) and limited fines in the base can be used in CPs applications as streets, low volume roads, parking lots, bus corridors (moderate rainfall) and any CP where the seals do not work well.