Evaluation of the Fresh Properties of Cement Pastes: Part I-Response Models Applied to Changes in the One-Variable-at-a-Time Method

The workability of cement-based materials is one of the features that makes these con struction materials the most used worldwide. Measuring and understanding how cement-based constituent materials affect fresh properties depends on the experimental plans. The experimental plans deal with the constituent materials used, the tests carried out, and the run of experiments. Here, the fresh properties (workability) of cement-based pastes are evaluated based on the diameter in the mini-slump test and the time in the Marsh funnel test being measured. This overall study is composed of two parts. In Part I, tests were carried out on several cement-based paste compositions incorporating distinct constituent materials. The effects of the distinct constituent materials on the workability were analyzed. Furthermore, this work deals with an approach to the run of experiments. A typical run of experiments was applied, with basic sets of mixed compositions being studied by only changing one input parameter at a time. This approach used in Part I is faced with a more scientific approach applied in Part II of the work where, based on the design of experiments, multiple input parameters were changed at a time. This work showed that a basic run of experiments is quick and easy to apply and leads to results for simple analyses; conversely, it lacks information for advanced analyses and scientific conclusions. The tests carried out included studies on the effect on the workability caused by changes in the limestone filler content, the type of cement, the water-to-cement ratio, distinct superplasticizers, and shrinkage-reducing admixture.info:eu-repo/semantics/publishedVersio

Incorporation of the sludge of sewage treatment plant on ceramic bricks manufacture: an exploratory study

Treatment processes used in most sewage treatment stations generate as by product a material named sludge. The amount of sludge grows proportionally with the increase in effluent collection and treatment services, which in turn must accompany population growth. The disposition of waste generated in an environmentally correct and economically viable way is one of the biggest challenges faced by companies that operate sanitation services. The ceramic industry presents a great potential for the use of this waste. The goal of this work was to evaluate the effect of the incorporation of the sewage sludge in the ceramic mass for the manufacture of solid bricks. The water absorption was lower for bricks with 10% sludge, but it increased for bricks with 15% sludge, resulting in products that presented water absorption slightly beyond of the limit of the standard NBR 15270. However, the results are promising because they show that additions of 10% or 15% sludge increased the compressive strength markedly.info:eu-repo/semantics/publishedVersio

Numerical methods to predict human induced vibrations on low frequency stairs. Part 1: literature review, modelling

Recent trends towards slender construction with prominent and exigent architectural requirements often result in low frequency staircases that are significantly flexible and susceptible to unacceptable vibrations, which may promote safety concerns for their users. For structural engineers, however, there is still a lack of understanding, available information and specific design guides for predicting the dynamic behaviour of staircases due to human induced vibrations. To address this problem, this work reviews and applies the main existing numerical methods for predicting vibrations, to evaluate their precision and provide practical guidance when designing flexible staircases. The work developed is presented in a two-part paper. In Part 1, the actual paper, several numerical methods are introduced and a detailed description is given of how these can be employed in a design stage. The distinction between low and high frequency staircases is explained, since it directly influences the structure’s behaviour and, subsequently, the selected method. A description is given of how to simulate walking dynamic loads, which forms the basis of all methods. The group effect is also discussed because it tends to considerably amplify the staircase response. Finally, the different numerical procedures are applied to a practical case and compared. It was observed that, although the four numerical methods were employed with the same staircase, their results were different. The reasons for the higher results of Fourier series walking models are explained. In Part 2, the follow-up paper, the numerical methods are employed on a real staircase, comparing the estimated and experimental results.info:eu-repo/semantics/publishedVersio

Experimental dataset from a central composite design to develop mortars with self-compacting properties and high early age strength

The concrete workability and the compressive strength are the principal properties of the fresh and hardened concrete, respectively. When self-compacting properties are required, scientific knowledge is important and appropriate models applied to achieve optimized compositions. Here, experimental data regarding to the mortars is presented. The dataset regards to a design of experiments carried out in mortars with commercial materials through a central composite design with five independent variables: Water(v)/Cement(v), Superplasticyzer(m)/Powder(v), Water(v)/Powder(v), Sand(v) /Mortar(v), FineSand(v)/Sand(v). In total 64 mortar composition were done: 25 factorial design consisting on 32 treatment combinations augmented by 10 axial runs plus 8 central runs, resulting in a central composite design with 50 mortar trial mix composition. Beside 14 extra mixes were done to allow comparing and validating results for the response models to be applied. Four dependent variables were measured: the D-flow and the t-funnel to measure the workability and the tensile strength and the compressive at the age of 24 h to assess the mechanical properties. Since the experiments were run based in a central composite design and extra mixes were prepared, response models can be applied to the dataset in order to find optimized mix compositions. (C) 2021 The Author(s). Published by Elsevier Inc