Browsing by Author "Lopez, Mauricio"
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- ItemAssessing Lightweight Aggregate Efficiency for Maximizing Internal Curing Performance(AMER CONCRETE INST, 2011) Paul, Alvaro; Lopez, MauricioInternal curing (IC), which has been extensively investigated in the last decade, has been shown to enhance hydration, diminish autogenous shrinkage, and mitigate early-age cracking due to self-desiccation in high-performance concrete. It also increases the internal porosity of concrete, however, which might reduce mechanical properties. Thus, a better understanding of what makes a lightweight aggregate (LWA) effective and efficient for IC is fundamental to maximize the gains and minimize the shortcomings.
- ItemAssessment of fire reaction and fire resistance of Guadua angustifolia kunth bamboo(ELSEVIER SCI LTD, 2012) Mena, Josue; Vera, Sergio; Correal, Juan F.; Lopez, MauricioThe main challenge for construction industry today is sustainability. Bamboo has properties that make it sustainable, but its fire behavior remains unknown. This paper presents an exploratory research on fire behavior of Guadua angustifolia kunth (a.k.) bamboo. Fire reaction was assessed through critical heat flux for ignition and flame spread while fire resistance through charring rate and strength variation with temperature. Fire reaction fall within standard limits used for structural woods, while fire resistance results are higher than that of plywood. Based on these preliminary results. Guadua a.k. would be adequate as structural and indoor finishing building material. (C) 2011 Elsevier Ltd. All rights reserved.
- ItemCharacterization of elastic and time-dependent deformations in high performance lightweight concrete by image analysis(PERGAMON-ELSEVIER SCIENCE LTD, 2009) Lopez, Mauricio; Kahn, Lawrence F.; Kurtis, Kimberly E.Image analysis and strain mapping were used to examine the nature of elastic, creep and shrinkage strains in high performance lightweight concrete (HPLC). The strain maps showed non-uniform deformations related to microstructural features. Both average strain and non-uniformity increased with time under testing. Paste-rich regions exhibited higher creep plus shrinkage than the lightweight aggregate (LWA) particles examined herein; it is suggested that LWA could have a role in reducing deformations of the paste. Compared to normal weight high performance concrete (HPC), the paste and LWA in the HPLC exhibited more gradual spatial differences in elastic deformations, creep and shrinkage. It is proposed that this difference results from the lower stiffness of the LWA compared to granite used in the HPC. The results indicate that improvement in elastic property matching between the lightweight aggregate and high performance paste reduces stress concentrations at the aggregate/paste interface and contributes to reductions in deformations of HPLC compared to HPC. (C) 2009 Elsevier Ltd. All rights reserved.
- ItemConcrete Containing Natural Pozzolans: New Challenges for Internal Curing(ASCE-AMER SOC CIVIL ENGINEERS, 2012) Espinoza Hijazin, Gaston; Paul, Alvaro; Lopez, MauricioNatural pozzolans (NP) have proven to be an effective supplementary cementitious material; however, the replacement of ordinary portland cement (OPC) with NP might increase the autogenous and drying shrinkage of concrete. Internal curing (IC) might be of great help when using NP because it can promote the pozzolanic reactions and reduce shrinkage. The aim of this research is to assess the effect of IC in concrete containing NP. Results indicate that a 39% replacement of OPC with NP decreased compressive strength by 15%, decreased chloride ion permeability by 66%, and increased autogenous shrinkage by 40%. IC with prewetted lightweight aggregate showed no significant effect in compressive strength or permeability, but it decreased autogenous shrinkage by up to 58%. NP used in this investigation presented higher chemical shrinkage than OPC, making IC less effective as levels of NP increased. The important decrease in permeability attained through the use of NP and the higher chemical shrinkage of NP makes IC a critical technology to consider in concrete mixtures with NP. DOI: 10.1061/(ASCE)MT.1943-5533.0000421. (C) 2012 American Society of Civil Engineers.
- ItemEffect of internally stored water on creep of high-performance concrete(AMER CONCRETE INST, 2008) Lopez, Mauricio; Kahn, Lawrence F.; Kurtis, Kimberly E.The effects of internally stored water on long-term deformations of high-performance concrete (HPC) were examined on 130 creep and shrinkage specimens and 750 compressive strength specimens. Creep and shrinkage were monitored for 500 days on sealed and unsealed concrete specimens using either normalweight or lightweight aggregate with different initial moisture conditions. The use of prewetted lightweight aggregate decreased creep by approximately 45% when compared with mixtures with air-dried lightweight aggregate. HPC with prewetted lightweight aggregate experienced creep that was 10% lower than that obtained in a similar HPC with normalweight granite aggregate. It is proposed that the reduction in creep with the prewetted lightweight aggregate is due to hydration enhancement, expansion afforded by internal curing, and by inhibition of water seepage.
- ItemExtending internal curing to concrete mixtures with W/C higher than 0.42(2011) Espinoza-Hijazin, Gaston; Lopez, MauricioInternal curing (IC) is an effective method for improving performance of low W/C - low permeability concretes because they require additional water to hydrate the cementitious materials. Conventional concretes, on the other hand, contain enough water to hydrate the cementitious materials, but are frequently not properly cured, allowing drying and compromising strength gain and durability. The aim of this investigation is to assess the effect of IC as a complement to traditional curing in relatively high W/C concretes (W/C above 0.42) under drying conditions. Degree of hydration, compressive strength, and permeability were measured in concretes with IC and without IC. Results show that even under drying conditions, mixtures with IC exhibit 16% higher hydration, 19% higher compressive strength, and 30% lower permeability than their counterparts with no IC. This suggests that IC can be very useful for improving performance in concrete mixtures with relatively high W/C under poor curing conditions. (C) 2010 Elsevier Ltd. All rights reserved.
- ItemNúmero Bilingüe Especial de Ingeniería en las Américas(2014) Lopez, Mauricio; Molenaar, Keith R.; Alarcon Cardenas, Luis Fernando; Schexnayder, Clifford J.
- ItemPredicting the evolution of static yield stress with time of blended cement paste through a machine learning approach(2023) Navarrete, Ivan; La Fe-Perdomo, Ivan; Ramos Grez, Jorge; Lopez, Mauricio
- ItemRelationship between digital development and subjective well-being in chilean school children(2021) Donoso, Gonzalo; Casas, Ferran; Carlos Oyanedel, Juan; Lopez, MauricioThis study explores how access, management and use of Information and Communication Technologies in secondary schools are related to the subjective well-being of adolescents. The central hypothesis of this work is that students attending schools with high digital development have higher levels of subjective well-being. To test this hypothesis, two quantitative empirical studies carried out in Chile are used as sources of information. The first one is the 2013 National Survey of School Well-being, applied to 15-year-old students (4964 cases) from 191 schools, and the second one is the 2012 National Census of Educational Computing. Subsequently, after both sources are merged, a descriptive analysis and an explanatory model are created based on the dependent variable Personal Wellbeing Index (PWI), and the independent variables School Digital Development Index (SDDI) and attributes of establishment and subjects. Among the results, the finding of a positive and significant relationship between school digital development and higher subjective well-being scores of students stands out.
- ItemReplacement of pozzolanic blended cement by supplementary cementitious materials: Mechanical and environmental approach(2023) Navarrete, Ivan; Valdes, Juan; Lopez, Mauricio; Vargas, FelipePozzolanic blended cements, used in several markets, can be mixed with supplementary cementitious materials (SCMs) to improve environmental performance keeping a similar compressive strength. Many SCMs are industrial byproducts that do not require intensive processing. Six industrial byproducts were studied as replacement of pozzolanic blended cement. Reactivity, compressive strength, and environmental performance were measured. Results showed that the use of SCMs as partial replacement for pozzolanic blended cement increases the reactivity of cement and, therefore, the compressive strength of cementitious pastes. Furthermore, environmental results showed beneficial or detrimental effects depending on replacement level, compressive strength, and CO2 footprint of each SCM.
- ItemSpecial Bilingual Issue on Engineering in the Americas(2014) Lopez, Mauricio; Molenaar, Keith R.; Alarcon Cardenas, Luis Fernando; Schexnayder, Clifford J.