Reproducible mini-slump test procedure for measuring the yield stress of cementitious pastes

The mini-slump test is a fast, inexpensive and widely adopted method for evaluating the workability of fresh cementitious pastes. However, this method lacks a standardised procedure for its experimental implementation, which is crucial to guarantee reproducibility and reliability of the test results. This study investigates and proposes a guideline procedure for mini-slump testing, focusing on the influence of key experimental (mixing and testing) parameters on the statistical performance of the results. The importance of preparation of always testing at the same time after mixing, testing each batch once rather than conducting multiple tests on a single batch of material, is highlighted. A set of alkali-activated fly ash-slag pastes, spanning from 1 to 75 Pa yield stresses, were used to validate the test method, by comparison of calculated yield stresses with the results obtained using a conventional vane viscometer. The proposed experimental procedure for mini-slump testing produces highly reproducible results, and the yield stress calculated from mini-slump values correlate very well with those measured by viscometer, in the case of fresh paste of pure shear flow. Mini-slump testing is a reliable method that can be utilised for the assessment of workability of cements

Characterising Concrete Mixes for 3D Printing

The 2nd RILEM International Conference on Concrete and Digital Fabrication, Eindhoven, The Netherlands (held online due to Coronavirus outbreak), 6-8 July 2020The construction industry is currently experiencing significant change as building information modeling (BIM), digital design and construction automation are exerting intense pressure on traditional technologies. As an advanced manufacturing technology, three-dimensional (3D) printing has significant potential applications in the construction sector, by utilizing a programmable robotic arm with a nozzle jet, 3D printing can enable us to construct complex concrete structures layer by layer. This new construction technique offers an advanced approach that can potentially accelerate the construction time and improve efficiency. They can work 24/7, even in a hazardous environment while minimising human errors. However, as an advanced cutting-edge technology, there are several remaining challenges to be overcome in comparison to traditional concrete casting, and these include appropriate pumpability, extrudability, buildability, compressive strength and open time for printing concrete. To overcome these challenges this project will investigate the effect of nanoclay to improve the fresh properties of printing concrete. It is considered that by utilizing different amounts of nanoclay and superplasticiser in the mix it will be possible to significantly affect the fresh properties of 3D printed concrete. Printable materials, like any other cementitious materials, flow only when submitted to stresses higher than a critical yield stress. In this project, a shear vane test was used to measure the yield stress of cement-based materials in the lab.University College Dubli

A Disease Without History? Evidence for the Antiquity of Head and Neck Cancers

There has been a long-running debate in anthropological, archaeological, and medical literature regarding the prevalence of cancer in various ancient human populations. At one extreme, some scholars have claimed that past human societies had rates of cancer roughly equivalent to those seen among modern peoples; at the other extreme, some researchers have effectively claimed that cancer is a disease of modernity. The present study aims to shed further light on this topic, at least insofar as cancers of the head and neck are concerned. A review of ancient art, medical texts, and paleopathological reports revealed somewhat discordant accounts of the age, geographical distribution, and prevalence of head and neck cancers. While representations of these neoplastic conditions in art are relatively rare and patchy in geographic distribution, descriptions of suspect lesions in ancient medical texts are rather more widespread, if unevenly distributed geographically, and the paleopathological record was found to contain surprisingly abundant evidence for cancers of the head and neck, especially as compared to what are, in modern societies, more ubiquitous cancers of the breast, lung, or prostate. While establishing the absolute prevalence of any of these conditions in antiquity is impossible, the present work establishes that cancers of the head and neck have long been present, and perhaps even prevalent, in human societies