Stepwise regression modeling for compressive strength of alkali-activated concrete

Alkali Activated ◽

Ambient Curing

This study investigated the influence of different curing conditions on the compressive strength (CS) of the different alkali activated concrete (AAC) specimens at the ages of 2, 28, and 90 days for the structural utilization and standardization process of AAC instead of OPC concrete. For this aim, 100% slag (S100), 75% slag and 25% fly ash (S75FA25), and 50% slag and 50% fly ash based (S50FA50) AAC specimens were produced. Based on the oven-curing (O), water-curing (W), and ambient-curing (A) methods, the influence of 2O for 2 days, 26A2O, 2O26A, 28A, 28W, 26W2O, and 2O26W for 28 days, and 88A2O, 2O88A, 90A, 88W2O, 2O88W, 90W for 90 days on the CS of the AAC were examined in details. In addition, the influence of delayed oven-curing conditions on CS development was also investigated. The results indicated that curing conditions significantly affected on the CS and the water-curing condition could provide a better CS for those of AAC at 90 days. Although, the oven-curing enhanced CS of the S100 specimens at initial ages (first oven-curing applied), delayed oven-curing (oven-curing applied later) was found significant for S75FA25 and S50FA50 specimens. The delayed oven-curing affected more on the CS of the AAC when fly ash content increased. The most of AAC specimens with oven-curing had significantly enhanced the CS at 28 days, but S50FA50 at the age of 90 days decreased. Different curing regimes were proposed for the superior compressive strength values for each AAC specimens at the ages of 28 and 90 days.

Rheological Characteristics of Alkali Activated Fly-Ash Concrete Mixtures

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.677.86 ◽

2016 ◽

Vol 677 ◽

pp. 86-92

Author(s):

Tomáš Váchal ◽

Rostislav Šulc ◽

Pavel Svoboda

Keyword(s):

Compressive Strength ◽

Fly Ash ◽

Fresh Concrete ◽

Rheological Characteristics ◽

Fresh Mixture ◽

Fly Ash Concrete ◽

Concrete Mixtures ◽

This paper describes rheological characteristics of concrete mixtures based on alkali-activated fly ash. There are shown relationships between workability of fly-ash fresh concrete mixtures and water–fly-ash ratio in fresh alkali-activated concrete. In addition, there is described relationship between workability in fresh mixture on compressive strength of alkali-activated concrete.

Effect of Specimen Size and Curing Condition on the Compressive Strength of Alkali-Activated Concrete

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/2629-02 ◽

2017 ◽

Vol 2629 (1) ◽

pp. 9-14 ◽

Cited By ~ 5

Author(s):

Robert James Thomas ◽

Sulapha Peethamparan

Keyword(s):

Compressive Strength ◽

Fly Ash ◽

Specimen Size ◽

Portland Cement Concrete ◽

Cement Concrete ◽

Slag Cement ◽

Fly Ash Concrete ◽

Activated Slag ◽

Alkali-activated concrete is a rapidly emerging sustainable alternative to portland cement concrete. The compressive strength behavior of alkali-activated concrete has been reported by various studies to a limited extent, but these discussions have been based on minimal evidence. Furthermore, although it is known that specimen size has a distinct effect on the apparent compressive strength of concrete, this effect has yet to be modeled for alkali-activated concrete. This paper presents the results of a comprehensive study of the effects of curing condition (i.e., moist-cured at ambient temperature for 28 days or heat-cured at 50çC for 48 h) and specimen size on the compressive strength of sodium silicate–activated fly ash and slag cement concrete. The heat-cured strength of alkali-activated slag cement concrete was linearly related to the moist-cured strength; the former was about 5% greater than the latter. Heat curing also improved the strength of alkali-activated fly ash concrete, although the effect was greatly magnified for lower-strength mixtures and was much less significant at higher strengths. Existing size effect laws employed for portland cement concrete proved reasonably accurate in describing the effect of specimen size on the apparent strength of alkali-activated slag cement concrete. However, these existing models greatly underestimated the size effect in alkali-activated fly ash concrete; the authors suggest that this finding was the result of significant microcracking in the alkali-activated fly ash concrete.

Development of Cementless Fly Ash Based Alkali-Activated Mortar

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.417-418.721 ◽

2009 ◽

Vol 417-418 ◽

pp. 721-724 ◽

Cited By ~ 1

Author(s):

Kyung Taek Koh ◽

Su Tae Kang ◽

Gum Sung Ryu ◽

Hyun Jin Kang ◽

Jang Hwa Lee

Keyword(s):

Compressive Strength ◽

High Temperature ◽

Fly Ash ◽

High Strength ◽

Molar Ratio ◽

Early Age ◽

Water Curing ◽

Curing Method ◽

This study investigates the effects of alkaline activators and curing method on the compressive strength of mortar for the development of cementless alkali-activated concrete using 100% of fly ash as binder. Results reveal that the compressive strength improved according to the increase of the molar concentration of NaOH. In addition, molar ratio Na2O to SiO2 of 1.12 activated the reaction of fly ash with Si and Al constituents and resulted in the most remarkable development of strength. In the case of mortar requiring high strength at early age, higher curing temperatures appeared to be advantages. Curing at 60°C during 48 hours is recommended for requiring high strength at age 28days. Moreover, performing atmospheric curing after high temperature curing appeared to be more effective for the development of strength than water curing. Based on these results, it has been analyzed that alkaline activators fabricated with proportions of 1:1 of 9M NaOH and sodium silicate should be used and that atmospheric curing should be performed after curing at 60°C during 48 hours to produce high strength alkali-activated mortar exhibiting compressive strength of 70MPa at age 28 days.

Strength and Acid Resistance of Ceramic-Based Self-Compacting Alkali-Activated Concrete: Optimizing and Predicting Assessment

Materials ◽

10.3390/ma14206208 ◽

2021 ◽

Vol 14 (20) ◽

pp. 6208

Author(s):

Hassan Amer Algaifi ◽

Mohammad Iqbal Khan ◽

Shahiron Shahidan ◽

Galal Fares ◽

Yassir M. Abbas ◽

...

Keyword(s):

Compressive Strength ◽

Acid Resistance ◽

Experimental Tests ◽

Strength Loss ◽

Control Specimen ◽

Ambient Conditions ◽

Acid Attack ◽

Ceramic Waste ◽

The development of self-compacting alkali-activated concrete (SCAAC) has become a hot topic in the scientific community; however, most of the existing literature focuses on the utilization of fly ash (FA), ground blast furnace slag (GBFS), silica fume (SF), and rice husk ash (RHA) as the binder. In this study, both the experimental and theoretical assessments using response surface methodology (RSM) were taken into account to optimize and predict the optimal content of ceramic waste powder (CWP) in GBFS-based self-compacting alkali-activated concrete, thus promoting the utilization of ceramic waste in construction engineering. Based on the suggested design array from the RSM model, experimental tests were first carried out to determine the optimum CWP content to achieve reasonable compressive, tensile, and flexural strengths in the SCAAC when exposed to ambient conditions, as well as to minimize its strength loss, weight loss, and UPVL upon exposure to acid attack. Based on the results, the optimum content of CWP that satisfied both the strength and durability aspects was 31%. In particular, a reasonable reduction in the compressive strength of 16% was recorded compared to that of the control specimen (without ceramic). Meanwhile, the compressive strength loss of SCAAC when exposed to acid attack minimized to 59.17%, which was lower than that of the control specimen (74.2%). Furthermore, the developed RSM models were found to be reliable and accurate, with minimum errors (RMSE < 1.337). In addition, a strong correlation (R > 0.99, R2 < 0.99, adj. R2 < 0.98) was observed between the predicted and actual data. Moreover, the significance of the models was also proven via ANOVA, in which p-values of less than 0.001 and high F-values were recorded for all equations.

Mechanical Properties of High Early Strength Class C Fly Ash-Based Alkali Activated Concrete

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/0361198120915892 ◽

2020 ◽

Vol 2674 (5) ◽

pp. 430-443

Author(s):

Eslam Gomaa ◽

Simon Sargon ◽

Cedric Kashosi ◽

Ahmed Gheni ◽

Mohamed A. ElGawady

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Strength Class ◽

Calcium Content ◽

Measured Data ◽

Strength Gain ◽

Conventional Concrete ◽

Class C ◽

This paper presents the mechanical properties of alkali activated concrete (AAC) cured at 70°C for 24 h. The AAC mixtures were synthesized using five class C fly ashes (FAs) having different chemical and physical properties. Sodium hydroxide (SS) and sodium silicate (SH) were used as the alkali activators in this study. A conventional concrete (CC) mixture, having a compressive strength of 34.5 MPa, was synthesized using ordinary Portland cement (OPC) mixture for comparison purposes. The slump, as well as the compressive, tensile splitting, and flexural strengths were investigated at different concrete ages up to 28 days. The results revealed that with increasing the calcium content in an FA used to synthesized AAC mixture, the slump value and the mechanical properties decreased. All AAC mixtures reached approximately 92% of their 28-day compressive strength after 1 day compared with only 29% in the case of CC. Therefore, AAC can be used in applications where rapid strength gain is required, such as urgent repair, precast industry, and so forth. The measured data was also used to develop a set of equations to accurately predict the splitting tensile and flexural strengths.

Preliminary Study of the Rheological and Mechanical Properties of Alkali-activated Concrete Based on Tungsten Mining Waste Mud

KnE Engineering ◽

10.18502/keg.v5i4.6801 ◽

2020 ◽

Author(s):

Abdelhakim Benhamouda ◽

João Castro-Gomes

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Portland Cement ◽

Rheological Behaviour ◽

Coarse Sand ◽

Mining Waste ◽

Binder Phase ◽

Portland Cement Concrete ◽

The rheological properties of Portland cement (PC) concrete have been extensively studied and compared with those of alkali-activated concrete (AAC). This study discusses the effect of the liquid to solid ratio on the rheological and mechanical properties of AAM concrete, based on mining waste mud as the binder phase, and compares them with those of Portland cement concrete (PCC). The AAM concrete studied is a mix of coarse aggregate 6/15, two types of sand (finer and coarse sand), and a precursor. The precursor is a mix of 70% tungsten mining waste mud, 15% waste glass and 15% metakaolin. This mix was activated by a combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) and the PCC was a mix of the same aggregate but with cement as binder and water as a liquid. The activator/precursor ratio was studied 0.5, 0.52, 0.54, 0.56 and 0.58. The results obtained show a similar rheological behaviour between AAC and PCC, the workability affected by L/S increases with the increasing ratio L/S in AAC and for L/S=0.5 slump was 6 cm and was 16 cm for L/S =0.58. Regarding the mechanical properties, the results obtained in 7 days showed similar performance in AAC and PCC. The compressive strength also decreases with the increasing of L/S, in AAC with L/S=0.5 the compressive strength was 15.9 MPa and for L/S =0.58 was 10.5. Keywords: Tungsten mining waste, Rheology, Mechanical properties, Portland cement, alkali-activated concrete

Stepwise regression modeling for compressive strength assessment of mortar containing metakaolin

International Journal of Modelling and Simulation ◽

10.1080/02286203.2017.1422096 ◽

2018 ◽

pp. 1-9 ◽

Cited By ~ 3

Author(s):

Mahmoud Hosseinpour ◽

Hojjat Sharifi ◽

Yasser Sharifi

Keyword(s):

Compressive Strength ◽

Stepwise Regression ◽

Regression Modeling ◽

Strength Assessment

CONSTITUTIVE MODELS FOR PREDICTING MECHANICAL PROPERTIES OF NATURAL POZZOLAN-BASED ALKALI ACTIVATED CONCRETE

Proceedings of International Structural Engineering and Construction ◽

10.14455/isec.res.2019.202 ◽

2019 ◽

Vol 6 (1) ◽

Author(s):

Mohammed Ibrahim ◽

Megat Azmi Megat Johari ◽

Muhammed Kalimur Rahman ◽

Mohammed Maslehuddin ◽

Hatim Dafalla Mohamed

Keyword(s):

Compressive Strength ◽

Flexural Strength ◽

Modulus Of Elasticity ◽

Constitutive Models ◽

Engineering Properties ◽

Strength Development ◽

Natural Pozzolan ◽

Material Development ◽

A large variety of mix design variables and environmental conditions in which alkali activated concretes (AAC) are cured, influences the nature and intensity of the binder formed. Equations developed for OPC-based concrete in various codes and published work may not accurately predict engineering properties of these AAC. AAC in this study was synthesized utilizing natural pozzolan (NP) in the presence of alkaline activators. Nano-SiO2 was added for enhancing the strength development at room temperature curing as NP is a low calcium precursor material. Development of compressive strength, flexural strength and modulus of elasticity were investigated. Using the data generated, two constitutive models, relating the compressive strength to flexural strength and modulus of elasticity were developed and compared with the equations specified in international codes for OPC-based concrete and previous studies in the area. The results show that the ACI 318, underestimates the flexural strength and overestimates the modulus of elasticity of alkali activated concrete. However, constitutive models developed in this study are in good agreement with the equations proposed in the previous works for AAC. Only the limited data available to date on the engineering properties of AAC cannot be used to establish robust constitutive relationships and more research is required in this area.

Experimental Study of the Dynamic Compressive and Tensile Strengths of Fly Ash and Slag Based Alkali-Activated Concrete Reinforced With Basalt Fibers

Frontiers in Materials ◽

10.3389/fmats.2021.651581 ◽

2021 ◽

Vol 8 ◽

Author(s):

Chong Lian ◽

Yubo Wang ◽

Shan Liu ◽

Yifei Hao

Keyword(s):

Tensile Strength ◽

Compressive Strength ◽

Fly Ash ◽

Portland Cement ◽

Strain Rate ◽

Dynamic Strength ◽

Test Results ◽

Complete Replacement ◽

The use of industrial by-products, e.g., fly ash, slag, as complete replacement of Portland cement to make alkali-activated concrete (AAC) has become a hot topic due to the contribution to sustainability in construction industry. AAC has comparable compressive strength compared to the ordinary Portland cement concrete (OPC) and has many advantages, such as excellent durability and corrosion resistance. However, similar to OPC, AACmaterial still has certain shortcomings such as brittleness, low tensile strength, and poor impact resistance, which can be improved by incorporating fibers in the matrix. This paper considers the basalt fiber-reinforced alkali-activated concrete (BFRAAC), and explores the dynamic compressive and tensile strengths through a series of impact tests. The test results show that the dynamic strength of BFRAAC exhibits significant strain rate effect, that is, the material strength increases with the strain rate. Compared to the compressive strength of the material, the strain rate sensitivity of its tensile strength is more marked. Based on the test results, empirical formulas describing the relation between dynamic strength and strain rate of BFRAAC are proposed.