Materiales de Construcción

Studying the hydration kinetics and mechanical-microstructural properties of Portland cements made with and without dredged sediment: experimental and numerical approaches

Tue, 11 Jun 2024 00:00:00 +0200

This research focused on two objectives: (i) investigating the impacts of sediment substitution in the raw meal on the hydration and mechanical-microstructural properties of cement; (ii) assessing the reliability of CEMHYD3D code for modeling the properties of hydrated cement. The experimental results indicated that a maximum rate of sediment up to 7.55% had no impact on the formation of mineralogical phases of clinker, the hydration and mechanical-microstructural development of cement. The degree of hydration and strengths of cement made of sediment substitution were slightly higher than those of reference cement, whereas the critical diameter of pores of both hydrated cements was nearly identical. Comparing the modeling results with the experimental measurements showed good predictions for the degree of hydration, hydration heat as well as strength development. However, the formation of hemi-and mono-carboaluminate phases was not predicted in the model, and the porosity prediction was also limited to the capillary porosity.

Influence of chemical pretreatment on the pozzolanicity of recycled glass microparticles used as a substitute for Portland cement

Thu, 23 May 2024 00:00:00 +0200

This research investigated the influence of using chemically treated glass microparticles as a partial replacement for cement in Portland cement pastes and mortars. The microparticles were obtained by grinding glass waste into three different particle size fractions (< 75 µm, < 45 µm, and < 25 µm), treated with calcium hydroxide (CH), and characterized using SEM/EDS and a laser particle size analyzer. Samples prepared with the incorporation of glass were characterized using XRD, TGA/DTG, and SEM/EDS. The pretreatment with calcium hydroxide induced the formation of C-S-H with different morphologies on the surface of the particles, in addition to causing changes in particle size distribution due to the formation of agglomerates. The pastes prepared with treated particles had lower amounts of CH and higher levels of hydrated silicates. However, when indirectly measuring the pozzolanicity of treated particles through the compressive strength of mortars, no significant differences were observed in the strengths of mortars made with treated and untreated particles.

Design of an explicit crack bridging constitutive model for engineered cementitious composites using polyvinyl alcohol (PVA) or polyethylene (PE) fiber

Z. Wang, B. Li, L. Li, Z. Zhang — Tue, 11 Jun 2024 00:00:00 +0200

This paper aims to establish an explicit crack bridging model that can link engineered cementitious composites (ECC) behavior from single fiber to single crack scale, which is great of designing ECC featuring pseudo tensile strain hardening and multiple cracks expanding by tailoring microstructure and materials selection. In this study, fiber bridging stress was divided into three parts including fiber bridging stress with no rupture, fiber debonding fracture stress, and fiber pullout fracture stress. Subsequently, the fundamental crack bridging model was emerged when fiber bridging stress with no rupture subtracted from the fiber rupture stress in debonding and pullout stage. Moreover, two-way pullout and Cook-Gordon effect were also considered to establish the complete model. It was found that the two-way pullout situation of polyvinyl alcohol (PVA) fiber has a significant influence on the crack opening width due to its slip hardening property, while the Cook-Gordon effect presents a faint crack width increment for PVA-ECC. However, the Cook-Gordon effect makes a significant contribution to the crack opening width of the composite produced by polyethylene (PE). This building intelligible model presents a better prediction for ECC through the comparison of experimental data or real average crack width in previous models, thus confirming the validity of this model.

Transport properties of fly ash-slag-based geopolymer concrete with 2M sodium hydroxide combined with variations in slag percentage, Al/Bi ratio, and SS/SH ratio

E.S. Sunarsih, S. As'ad, A.R. Mohd.Sam, S.A. Kristiawan — Thu, 23 May 2024 00:00:00 +0200

The aim of this research is to determine the effect of sodium hydroxide molarity 2M combined with variations in slag percentage, ratio of alkali activator to binder (Al/Bi), and ratio of sodium silicate to sodium hydroxide (SS/SH) on the transport properties of fly ash-slag-based GPC cured at ambient temperature. The result is increase in slag percentage and SS/SH ratio lead to a decrease in porosity, water absorption rate and chloride permeability. The alkali activator to binder (Al/Bi) ratio of 0.45 produces the lowest porosity, water absorption rate, and chloride permeability. The porosity, sorptivity, and chloride penetration depths of all GPC are lower than those of OPC. The recommended mix compositions for GPC that exhibit lower transport properties than OPC are GPC4 (slag 40%, SS/SH ratio 1.5, Al/Bi ratio 0.45); GPC5 (slag 50%, SS/SH ratio 1.5, Al/Bi ratio 0.45); and GPC7 (slag 30%, SS/SH ratio 2.0, Al/Bi ratio 0.45).

Effect of recycled fine powder as a calcium source on fresh and hardened properties of geopolymer mortar

A. Sharma, P. Singh, K. Kapoor — Mon, 03 Jun 2024 00:00:00 +0200

This study explores the efficacy of Recycled Fine Powder (RFP) derived from construction and demolition waste as a sustainable substitute for Ordinary Portland Cement (OPC) as a Calcium (Ca) source in geopolymer mortar. Fresh properties of Geopolymer Mortar (GPM) were evaluated in terms of slump-flow, initial-final setting time, whereas hardened properties were evaluated in terms of Compressive Strength (CS), Water Absorption (WA), porosity, acid attack, and dry shrinkage at both ambient and heat curing. Results indicate that the RFP performs well in all mixes. However, mix C10R10 shows the overall best results, as 17% higher compressive strength was observed as compared to mix C20R0, which further increases to 88% when compared to mix C0R0. Thus, RFP provides sufficient Ca content as an activator in GPM.

The effects of synthetic wollastonite microfibers on PVA fiber-reinforced engineered geopolymer composites

H.Ö. Öz, M. Güneş — Thu, 23 May 2024 00:00:00 +0200

In this study, first, synthetic wollastonite microfiber (SWM) with a high aspect ratio (44:1) was produced with a special three-stage production method. Then, fly ash and ground granulated blast furnace slag-based engineered geopolymer composites (FA+GGBFS-based EGCs) were developed. SWM was used in different proportions instead of FA. The compressive strength of EGCs, changed in the range of 88.1-111.1 and 95.1-122.6 MPa at 7 and 28 days, respectively. Additionally, EGCs containing 6% SWM performed the best, considering both ‘‘increasing deformation capacity’’ and ‘‘maintaining the bearing strength by fiber bridging after crack’’, since they acted like a fiber owing to the acicular particle structure of SWM. Moreover, it can be said that the presence of the SWM mineral in the pore system, ensured pore discontinuities in the matrix because of its acicular particle structure. Consequently, the mechanical, durability and dimensional stability properties of EGCs improved with SWM.

Environmental benefits of microwave-assisted self-healing technology for pavements - A Life Cycle Assessment comparative study

A.M. Rodríguez-Alloza, F. Gulisano, D. Garraín — Thu, 23 May 2024 00:00:00 +0200

The maintenance and rehabilitation of roads is becoming a key challenge in the pavement industry to decrease the consumption of natural resources. Microwave-assisted self-healing technology extends the life-service of asphalt pavements for roads reducing the need for fossil fuels over its lifespan and saving the use of natural resources. This technique takes advantage of the thermoplastic and dielectric properties of asphalt mixtures that allows cracks to be closed, hence, heal and restore the asphalt mixtures mechanical behaviour without implementing more invasive traditional maintenance operations like milling and replacing the pavement. A Life-Cycle Assessment was carried out to determine the potential environmental benefits of using this technology quantifying its potential environmental impacts. Different scenarios in which the heating energy and the addition of slag varies has been evaluated and compared with a conventional road. Results shows that this technology could decrease a significant number of environmental impacts over the lifecycle.

Shear behavior of hollow clay brick masonry wallet coated with short jute fiber reinforced mortar

L.N. Farias, P.R.L. Lima, R.D. Toledo Filho — Thu, 23 May 2024 00:00:00 +0200

The objective of this study is to present a new method of reinforcing masonry using layers of mortar reinforced with short jute fibers. Mortars were produced with 0%, 2% and 3% jute fibers with cementitious matrices free of calcium hydroxide. The effectiveness of the reinforced mortar was evaluated through diagonal compression tests of hollow ceramic brick masonry prisms. The prisms were coated on both sides. The experimental results demonstrated that the diagonal resistance of the fiber system increased by 28 to 30% and presented greater resistance to elastic deformation during load application, with deformation coefficients 2 and 3 times greater for 2% and 3% of fibers, respectively. Therefore, jute fibers prove to be a sustainable and efficient alternative for masonry reinforcement applications, with maximum applied loads considerably higher than the unreinforced system, in addition to better crack control.