Industrial Low-Clinker Precast Elements Using Recycled Aggregates

ABSTRACT: ncreasing amounts of sustainable concretes are being used as society becomes more aware of the environment. This paper attempts to evaluate the properties of precast concrete elements formed with recycled coarse aggregate and low clinker content cement using recycled additions. To this end, six different mix proportions were characterized: a reference concrete; 2 concretes with 25%wt. and 50%wt. substitution of coarse aggregate made using mixed construction and demolition wastes; and others with recycled cement with low clinker content. The compressive strength, the elastic modulus, and the durability indicator decrease with the proportions of recycled aggregate replacing aggregate, and it is accentuated with the incorporation of recycled cement. However, all the precast elements tested show good performance with slight reduction in the mechanical properties. To confirm the appropriate behaviour of New Jersey precast barriers, a test that simulated the impact of a vehicle was carried out.This research was funded by SODERCAN, S.A. (SODERCAN/FEDER) and BIA2013-48876-C3-2-R awarded by the Ministry of Science and Innovation

Influencia de la fracción mixta y de hormigón en las prestaciones mecánicas de los hormigones reciclados

[ES] La utilización de áridos reciclados en el ámbito de la ingeniería civil ha incrementado en los últimos años, representando en 2014 un 8% de la producción total de áridos a nivel europeo. La actual Instrucción Española de Hormigón Estructural (EHE-08) permite la incorporación parcial (< 20% peso) de áridos reciclados gruesos de hormigón como sustitutos de los áridos convencionales. El presente trabajo de investigación persigue analizar el efecto de utilizar simultáneamente la incorporación parcial (50%) de arena reciclada (hormigón o mixta) con árido grueso reciclado de hormigón (50%) en las prestaciones finales de los hormigones reciclados con fines estructurales. Para alcanzar este ítem, se caracterizó primeramente los áridos empleados, para posteriormente proceder al diseño y fabricación de las mezclas objeto de estudio. A continuación, se llevó a cabo la caracterización física (densidad y consistencia) y mecánicas (compresión, tracción y flexión) de los nuevos hormigones. Resultado de este estudio se observa que la incorporación de la fracción fina y gruesa reciclada no afecta nocivamente en las prestaciones finales de los mismos pudiendo ser empleados en el sector de la construcción y contribuyendo al actual modelo de economía circular.Este estudio ha sido realizado gracias a la financiación de los proyectos de investigación BIA 2013-48876-C3-1-R, BIA 2013-48876-C3-2-R y BIA2016-76643-C3-1-R concedidos por el Ministerio de Ciencias e Innovación, así como por la ayuda GR-15064 concedida al grupo de investigación MATERIA por parte de la Junta de Extremadura y el Fondo Europeo de Desarrollo Regional – FEDER.Medina, C.; Plaza, P.; Velardo, P.; Matías, A.; Sánchez De Rojas, M.; Sáez Del Bosque, I. (2018). Influencia de la fracción mixta y de hormigón en las prestaciones mecánicas de los hormigones reciclados. En HAC 2018. V Congreso Iberoamericano de hormigón autocompactable y hormigones especiales. Editorial Universitat Politècnica de València. 691-700. https://doi.org/10.4995/HAC2018.2018.6447OCS69170

Hydration of water- and alkali-activated white Portland cement pastes and blends with low-calcium pulverized fuel ash

Pastes of white Portland cement (wPc) and wPc-pulverized fuel ash (pfa) blends were studied up to 13 years. The reaction of wPc with water was initially retarded in the presence of pfa particles but accelerated at intermediate ages. Reaction with KOH solution was rapid with or without pfa. A universal compositional relationship exists for the C-A-S-H in blends of Pc with aluminosilicate-rich SCMs. The average length of aluminosilicate anions increased with age and increasing Al/Ca and Si/Ca; greater lengthening in the blends was due to additional Al3+ at bridging sites. The morphology of outer product C-A-S-H was always foil-like with KOH solution, regardless of chemical composition, but with water it had fibrillar morphology at high Ca/(Si+Al) ratios and foil-like morphology started to appear at Ca/(Si+Al) ≈1.2-1.3, which from the literature appears to coincide with changes in the pore solution. Foil-like morphology cannot be associated with entirely T-based structure

Modificaciones nanoestructurales en pastas de cemento

Tesis doctoral inédita, leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Física Aplicada. Fecha de lectura: 17-07-201

Calorimetric study of white portland cement hydration. Effect of nanosilica and temperature

Cement manufacture generates environmental problems due, among others, to the greenhouse gases, especially CO2, emitted in the process. A number of materials have been used as cement additions in recent years to lower such emissions. One of the foremost is nanosilica (nSA), which as a nano-filler and pozzolan enhances the mechanical strength and reduces the porosity of the end product. Portland cement hydration is favoured by both temperature and the presence of nSA. Calorimetric studies were performed to monitor the early age hydration of white portland cement containing 10 % nSA at 25, 40 and 65 ºC for 24 h. After hydration was detained at trial times defined by the peaks observed on the calorimetric curves, samples cured for those times were characterised by XRD, DTA/TG, and 27Al MAS NMR. The findings showed that temperature and the addition of nSA induced the same type of alterations in the calorimetric curve: the induction period was shortened and heat flow rose. The calorimetric curve for the nSA-containing pastes cured at 65 ºC exhibited 3 main peaks, one more than the curve for the sample without nSA. Moreover, the ratios between the intensities of the signals varied widely. Nanosilica stabilised ettringite in the samples hydrated at 65 ºC, while that phase was non-existent in the samples without nSA.ICCC 2015, Beijing, China, 13~16 October 2015; http://iccc2015.csp.escience.cn/dct/page/1Peer Reviewe

Caracterización de nuevos materiales cementantes

Jornadas Internacionales de Investigación en Construcción Eduardo Torroja, Madrid, 21-22 Noviembre 2013. http://www.fundacioneduardotorroja.org/index.php/es/noticias/227-jornadas-internacionales-de-investigacion-en-construccion.htmlPeer Reviewe

Effect of temperature on C–S–H gel nanostructure in white cement

12 pags. ; 11 figs. ; 5 tabs.© 2013, RILEM. Different ages of white cement pastes hydrated at 100 % RH and 25 or 65 °C were characterised with 29Si MAS NMR spectroscopy. The findings showed that raising the curing temperature from 25 to 65 °C accelerated hydration of the belite phase considerably, inducing a sixfold rise in its one day degree of hydration, while alite phase hydration grew by a factor of only 1.5 in the first day. Moreover, the C–S–H gel formed at the higher temperature had a longer mean chain length and a higher initial uptake of Al3+. Lastly, curing at a higher temperature stabilised only one crystalline aluminate phases, calcium hemicarboaluminate.This research was funded by the Spanish Ministry of Education and Science (MAT2006-11705, CONSOLIDER: CSD2007-00058 and PIE: 201160E103) and the Regional Government of Madrid (Geomaterials Programme, S2009/MAT-1629). Research fellowship BES-2007-16686 is gratefully acknowledgedPeer Reviewe

Role of organic admixtures on thaumasite precipitation

Thaumasite formation is normally a slow process; however some studies have shown that the presence of sucrose promotes its formation substantially. Many of today's concretes contain organic admixtures and no research has been conducted to date to determine whether the presence of these admixtures may induce or favour thaumasite formation. The present study aimed to ascertain whether, like sucrose, admixtures may further that process, and to propose a working methodology to do so. The methodology used was: mixing sodium carbonate, sulfate and silicate solutions with a CaO solution with eleven commercial admixtures. The precipitates obtained after different curing times (up to 1 year) and temperatures (5 and 25 °C) were characterised with FTIR and XRD. It was possible to distinguish between admixtures that did and those that did not favour thaumasite formation, i.e., products containing lignosulfonates or a mix of sodium carboxylate and polysulfonate as well as aluminium-based accelerating admixtures favoured thaumasite formation.Peer reviewe

Combined effect of amorphous nanosilica and temperature on white Portland cement hydration

White cement pastes were hydrated in the presence or absence of amorphous nanosilica (nSA) and cured at 25 or 65°C. The findings showed that at the higher curing temperature the initial belite hydration rate rose substantially and that this effect was more accentuated in the pastes containing nSA. The C-S-H gel formed in the presence of nSA was more uniform and had a consistently longer mean chain length (MCL) than in the gels formed in the absence of the addition. Moreover, the C-S-H gel formed in nSA-bearing paste cured at the higher temperature had a longer MCL and a higher Al3+ uptake than the gels in the other pastes studied. Lastly, at 65°C, the presence of nSA stabilized ettringite formation during the first 28 days of paste hydration; while no calcium hemicarboaluminate, which was the sole crystalline aluminate hydrate identified in the unblended pastes, was detected in the nSA-containing pastes. © 2013 American Chemical Society.This research was funded by the Spanish Ministry of Education and Science (Grants MAT2006-11705 and CONSOLIDER CSD2007-00058), the Agencia Estatal Consejo Superior de Investigaciones Cientifícas (Grant PIE: 201160E103), and theRegional Government of Madrid (Geomaterials Programme, Grant S2009/MAT-1629). Research fellowship BES-2007- 16686 is gratefully acknowledged.Peer Reviewe