Search

The main aim of this work is to comparatively reveal the effect of fibre type, length and content on compressive strength and microstructure of structural geopolymer concrete (GPC) produced under constant mixture and curing parameters in order to address the significant gap in present literature. Firstly, GPCs with different NaOH concentrations (i.e., 6, 9, 12 and 15 M) and activator solution/binder (a/b) ratios (i.e., 0.45 and 0.55) were produced in ambient curing condition, and optimum production parameters were determined based on the preliminary evaluations. Then, glass and polypropylene fibres in 6‐mm length (GS6 and PP6) and polyamide and polypropylene fibres in 12‐mm length (PY12 and PP12) were included in GPCs at ratio of 0.4%, 0.8% and 1.2% (by volume). Compressive strength, apparent porosity, bulk density, ultrasonic pulse velocity (UPV), X‐ray diffraction (XRD) and scanning electron microscope (SEM) analysis of GPC samples were carried out comparatively. The inclusion of GS6 fibre enhanced the compressive strength thanks to fibre surface being covered by geopolymer gel and the strong adhesion between GS fibre and geopolymer matrix. SEM images of fibre reinforced GPC (FRGPC) also confirmed the experimental findings, which were attributed to improvement in compressive strength. Regardless of the fibre type, the maximum compressive value strength was obtained from GPC specimens with 0.4% fibre and then decreased. Higher fibre inclusions led to poor compaction, workability issues and inhomogeneous fibre dispersions. A very good relation (R2 = 0.98) was acquired between UPV and compressive strength values of GPC/FRGPC samples. [ABSTRACT FROM AUTHOR]

In this study, a new grouting composite, called geopolymer grout, with high compressive strength (> 107 MPa, cured at ambient conditions) was developed and injected into damaged reinforced concrete (RC) beam. This investigation was planned in two steps: (1) determination of optimum geopolymer grout composite depending on viscosity, compressive strength, and SEM findings; (2) injection of optimum geopolymer grout to damaged RC beam. Geopolymer grouts were fabricated with different NaOH concentrations (i.e., 8, 10, and 12 M) and Ca(OH)2 contents (1, 3, 5 and 7% of slag weight). A remarkable advance in fresh and hardened characteristics of geopolymer grouts was acquired with changing of NaOH concentration and Ca(OH)2 content. A reference RC beam was subjected to bending test and the load–displacement curve was obtained. The determined optimum geopolymer grout was injected into this damaged RC beam and exposed to reloading test. The strengthened RC beam specimen was compared with reference RC beam in terms of failure modes, load capacity and crack patterns. After damaged RC beam was strengthened, it showed higher mechanical performance compared to reference RC beam. The experimental findings revealed that geopolymer grouts could be a suitable alternative for repair and strengthening of damaged RC beam due to their low viscosity, eco-friendliness, good bonding and superior compressive strength. [ABSTRACT FROM AUTHOR]

A comprehensive experimental study was conducted to investigate effect of different production parameters such as activator type, activator concentration and curing temperature on fresh and hardened properties of volcanic tuff based geopolymer paste (GP) samples. Volcanic tuff obtained from Nevşehir (Central Anatolia, Turkey) was ground to particle size less than 45 μm, after that alkali activation process was provided with two type of alkali activators such as NaOH and NaOH+Na2SiO3 (SH and SH + SS) solutions. Produced geopolymer samples were cured at different temperatures ranging from 23 to 150°C. Compressive strength, setting time, hydration heat of GP samples were investigated. Additionally, microstructural investigations were performed with SEM and XRD analyzes. As a result of modification of experimental parameters, compressive strength development reached to 41.43 MPa was obtained from GP samples, which did not harden in laboratory conditions. It was also determined that the alkali activation of volcanic tuff with SH exhibited better mechanical and microstructural properties than alkali activation with SH + SS. [ABSTRACT FROM AUTHOR]

• This paper aims to improve elevated temperature performances of geopolymer concrete. • Nano-silica and micro-silica additives increased elevated temperature resistance. • Additives reduced crack formation. • Additives decreased water absorption compared to the reference geopolymer sample. Geopolymer binders (GPBs) have gained an increasing research potential in recent years due to their environmental, economic and durability advantages. This paper aims to improve elevated temperature performances of volcanic tuff (VT) based geopolymer concrete (GPC) by utilizing nano-silica (NS), micro-silica (MS) and styrene-butadiene latex (SBL). To this end, NS, MS and SBL additives were added to GPC samples at 2%, 2% and 5% ratios by weight of binder, respectively. GPB was obtained by activating ground VT with 12 M NaOH solution. Produced GPC samples were exposed to elevated temperatures (100, 300, 500 and 700 °C) for 1 h after reaching the target temperature. Changes in compressive strength, water absorption, visual appearance, weight and microstructure of GPC samples were investigated after the influence of elevated temperatures. The experimental findings displayed that compressive strength of GPCs increased up to 300 °C independently of the type of additive used, but higher temperatures than 300 °C caused decrease in compressive strength values. As a result of mechanical tests and microstructure investigations, it was determined that MS additive significantly increased the elevated temperature performance of GPCs. Additionally, color of GPC samples turned gray after elevated temperatures due to dehydration of GPB and microstructural transformations occurring in aggregates. [ABSTRACT FROM AUTHOR]

Highlights • Two different activation methods were used to produce geopolymer concrete. • Different additives were selected to improve properties of GPC samples. • Optimum additive ratios have been determined for each conducted test. • The activation method with NaOH led to superior mechanical properties. • In terms of FT resistance, the activation method of Na 2 SiO 3 + NaOH was advantaged. Abstract This study aims to the improvement of volcanic tuff-based geopolymer concrete (GPC) with the addition of nano silica (NS), micro silica (MS) and Styrene-Butadiene Latex (SBL) at the different ratios. For this purpose, incorporating of volcanic tuff with NS (1, 2, 3%), MS (1, 3, 5%) and SBL (5, 10, 15%) was provided. GPC samples were produced with two different activation method (Na 2 SiO 3 + NaOH and sole NaOH). 28-day compressive strength, freeze-thaw (FT) resistance, microstructure, water absorption, density, bulk density and apparent porosity values of volcanic tuff-based GPC samples were investigated. The results indicated that the compressive strength of NaOH-activated samples was much higher than similar ones activated with Na 2 SiO 3 + NaOH. In both activation methods, the optimum NS and SBL ratios were determined as 2% and 5%, respectively. Also, the optimum additive of MS ratio was determined 5% and 3% for Na 2 SiO 3 + NaOH and sole NaOH-activated samples, respectively. As well as the highest compressive strength losses as a result of 300 FT cycles were observed in pure samples for both activation methods, Na 2 SiO 3 + NaOH-activated samples exhibited better resistance to FT effect than similar ones activated with sole NaOH. [ABSTRACT FROM AUTHOR]

Many researches have been done to investigate using raw materials in the production of geopolymer cements. This paper presents the effects of alkali dosage and silica modulus when using sodium metasilicate solution at different curing conditions on the geopolymerization of ferrochrome slag (FS). As alkali activation for geopolymerization, NaOH and Na 2 SiO 3 solution were used. Geopolymer cement was produced using FS as raw material with 3 different silica modulus (0.50, 0.60 and 0.70) and 4 different Na 2 O concentrations (4%, 7%, 10% and 12%). The setting time, hydration heat and compressive strength of geopolymer paste samples and compressive strength of geopolymer mortar samples were obtained. The setting time varied between 120 and 870 min, it showed variability depending on Na 2 O content. The highest 28 day compressive strength of the geopolymer paste samples was obtained from one with Na 2 O concentration of 7% and silica modulus of 0.70. Geopolymer mortars were prepared for the determination of compressive strength by adding FS:sand:alkali activator ratio 1:2:0.30, 0.35 and 0.40. The specimens were cured at 60 °C and 80 °C kept for 20 h and the other mortar samples were stored under laboratory conditions. Compressive strength of the material decreased, when w/b (water/binder) ratio increased. The highest 28 day strength of the geopolymer mortar was obtained at 0.30 w/b ratio and laboratory temperature curing conditions. The hydration heat of geopolymer paste samples was found to be less than normal Portland cements. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were investigated to study the microstructural properties of the geopolymers. [ABSTRACT FROM AUTHOR]