portland cement concrete
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CivilEng ◽  
2022 ◽  
Vol 3 (1) ◽  
pp. 51-65
Author(s):  
Rodrigo Antunes

This study investigates the high contents of cementitious materials in Portland cement concrete and assesses the required (f’cr) and actual (σ) compressive strength of concrete specimens. A linear optimization technique identifies the required binder content to reach f’cr. Standard specifications have required concrete overdesign (OD) for decades, but few studies have evaluated the actual magnitude of OD from field data. The compressive strength of 958 cylinders prepared in the field represented 8200 m3 of ready-mixed concrete with 300 and 450 kg/m3 of cementitious are analyzed. The actual OD appears to be 7 to 21% higher than required. The required 28-day compressive strength of concrete was achieved in less than seven days. Therefore, the content of the cementitious materials could be reduced by 6 and 17% so that concrete could reach f’cr without cementitious overconsumption. Reducing cementitious content is recommended to improve construction quality and optimize resource utilization. Among the main reasons for this recommendation are the estimated substantial long-term savings, increased concrete durability and more rational use of natural resources required to build the structures.


Author(s):  
Leandro Silva de Assis ◽  
Joaquim Teixeira de Assis ◽  
José Renato de Castro Pessoa ◽  
Armando Dias Tavares Júnior

Abstract This work aims to present a methodology for the elaboration of a deformation map in a Portland cement concrete specimen to predict fractures caused by axial compression stresses, using the technique of Digital Image Correlation - DIC 2D. For this purpose, 5 concrete specimens with compressive strength expected at 28 days fck of 40 MPa were analyzed, which were tested in the ABNT NBR 5739/2018 standard - compression test of cylindrical concrete specimens. During the test, the necessary digital images were acquired in the DIC-2D array. These images were subsequently processed, and the results interpreted statistically. According to the result of the correlation of images obtained, it was found that 67% of the specimens had regions of accumulation of stresses that indicated in advance the location of the rupture, which enabled the development of a fracture prediction map. The results obtained in the research showed that the methodology used by means of the DIC-2D arrangement was able to predict the place where the rupture in the specimens occurred.


2021 ◽  
Author(s):  
Carl Lenngren ◽  
Maria Hernandez

Asset management of infrastructure is fundamental for maintenance planning and preservation of common property. A robust testing program is needed to assess the present-day status and for proper actions in time to minimize the ongoing depreciation of value. As a matter of fact, Portland Cement Concrete pavements show very little deterioration even after many years in service. Thus, it may be difficult to accurately predict the present asset value, other than using linear relations to the presumed design life. The primary reason for failure is cracking in concrete pavements, so assessing the dissipated energy from the load-deformation relation from a given load could be utilized for the purpose. The dissipated energy, i.e. the work data can be assessed by a falling weight deflectometer test, mimicking the passing of a truck or aircraft wheel load. In the present study, dynamic field data are evaluated, and the input data needed for the fracture mechanics model are used to predict the pavement life regarding cracking. To predict fracture energy and assess rolling resistance as well in concrete pavements, we need to consider the energy balance of the pavement system. To assess dissipated energy, falling weight deflectometer time histories are used to evaluate the pavement contribution to rolling resistance. Such analyses include all layers in the structure including the subgrade, so in the present case a way of sorting the dissipation at various depths is investigated. Field data were collected from a site, at mid-life of the predicted design life. The failure was confirmed several years later, and the remaining life was compared with the assumption that the dissipated energy near the edge was enough to initiate the cracks within the actual time to failure. Conversely, the dissipation at the mid-slab position was below the limit. The data from the field test were also used as an input for a finite element model to see if it was viable to further improve the prediction. The method seems to be promising, but more data are needed as the present set only represents the mid-life status.


2021 ◽  
pp. 1-29
Author(s):  
Himabindu Myadaraboina ◽  
David Law ◽  
Indubhushan Patanikuni

The incorporation of high volume fly ash, up to 80%, in concrete without compromising the mechanical and durability properties is potentially very advantageous to the concrete industry in enabling the delivery of economic, social and environmental benefits. To assess this, two high volume fly ash mix designs incorporating 80% class F ultra-fine fly ash, known as microash and hydrated lime, with 10% silica fume and 0 % silica fume have been investigated. Properties investigated are compressive strength, carbonation, chloride ion penetration, water absorption and permeability. The specimens were cured for a maximum period of 90 days to optimize completion of the hydration reaction. The results show that the concrete manufactured with 80% microash exhibited compressive strength in excess of 40 MPa at 28 days and over 70 MPa at 90 days. The material also displayed excellent durability properties compared to the normal Portland cement concrete and other high volume fly ash concretes. The addition of silica fume improved the strength and durability properties of the material.


Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7642
Author(s):  
Ivan Francklin ◽  
Rogério Pinto Ribeiro ◽  
Fernando Augusto Corrêa

The main objective was to determine the deleterious potential of quartzite mining tailings subjected to different ASR alkali–silica reaction tests. The studies included petrographic analysis, chemical analysis of cements, expansion tests in mortar bars and concrete prisms, and microstructural analysis. Petrographic analysis of quartzites indicated high percentages of deformed quartz (95%), and were classified as potentially reactive. Two types of HES high early strength cement with alkaline equivalents of 0.749% and 0.61%, respectively, were selected. Of the 8 samples analyzed by the accelerated method in mortars, only 2 quartzite samples and 1 diabasium sample indicated potentially reactive behavior. The accelerated and long-term methods in concrete prisms proved to be effective and were consistent with the deleterious potential of the samples. All analyzed samples were diagnosed with the ASR gel. In the microstructural analysis, in addition to the ASR products, other expansive products of late ettringite were detected. Reaction mitigation methods are proposed so that quartzite waste can be used as an alternative aggregate in concrete, and thus contribute to the reduction of mine tailings and, consequently, reduce the negative environmental impact from mining.


2021 ◽  
Vol 11 (22) ◽  
pp. 10868
Author(s):  
Ionut-Ovidiu Toma ◽  
Sergiu-Mihai Alexa-Stratulat ◽  
Petru Mihai ◽  
Ana-Maria Toma ◽  
George Taranu

The paper presents the results of a research work aimed at assessing the long-term strength and elastic properties of rubberized concrete. The parameters of the research were the rubber replacement of fine aggregates and the age of testing the specimens. Compressive and splitting tensile strength of concrete cylinders were obtained at the age of 5 years, coupled with the static and dynamic modulus of elasticity of all concrete specimens. Additionally, the material damping coefficient was assessed by means of non-destructive tests. The density of the rubberized concrete decreases with the percentage replacement of natural sand by rubber aggregates. A significant drop in the values of density after 5 years was observed for specimens made with rubberized concrete. The static and the dynamic moduli of elasticity decrease with the increase in rubber content. A similar trend is observed for the compressive and tensile splitting strength.


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