CONSTRUCTION AND BUILDING MATERIALS (Elsevier Ltd.)
Assessment of consistency and strength properties of clays treated with paper sludge ash-based stabilizers using the water absorption and retention rate
Binh Nguyen Phan, Ryo Sekine, Kimitoshi Hayano, Hiromoto Yamauchi
CONSTRUCTION AND BUILDING MATERIALS, Volume 351, 10 October 2022
(https://doi.org/10.1016/j.conbuildmat.2022.128936)
Abstract
Paper sludge ash-based stabilizers (PSASs) have recently been developed in Japan as sustainable construction materials for soil stabilization. PSASs are produced by the in-solubilization of heavy metals in paper sludge (PS), which is generated as a by-product of the de-inking and re-pulping of paper. PSASs can improve the stability of high-water-content clays immediately after mixing owing to their good water absorption and retention performance. However, mixture design methods that consider time variations of the water absorption and retention performance of a PSAS are lacking. Therefore, in this study, the effects of a PSAS on the physical and mechanical properties of the treated clay were experimentally investigated, considering the change in the water absorption and retention performance of the PSAS with curing time. The water absorption and retention rate, Wab, of the PSAS, is defined as the ratio of the mass of water absorbed and retained by the PSAS to its dry mass. Physical tests and cone index tests were conducted on different types of clays treated with different types of PSASs. The test results showed that different Wab values were obtained depending on the type of the PSAS and that the Wab value increased with curing time. From the experiments, it was found that the liquid limits, wL, and plastic limits, wP, of the PSAS-treated clays with different curing times could be evaluated from the Wab values of the PSAS and the particle sizes of the PSAS and untreated clays. A clear correlation was also found between the cone index, qc, and liquidity index, IL, of the treated and untreated clays. Based on the results, a new approach for mixture design was proposed. The applicability of the proposed method was investigated, and the results showed that the measured qc value of the PSAS-treated clay was close to the target qc value. The average measured qc was approximately 1.1 times the corresponding target qc. The maximum error between the measured qc and target qc values was approximately 30%.
An analytical investigation of bond deterioration between rebar and ASR/DEF-damaged concrete with and without stirrup confinement using 3D RBSM
Jie Luo, Shingo Asamoto, Kohei Nagai
CONSTRUCTION AND BUILDING MATERIALS, Volume 351, 10 October 2022
(https://doi.org/10.1016/j.conbuildmat.2022.128923)
Abstract
The bond performance between rebar and concrete is essential for the safety of RC structures. There is a need for research on bond deterioration due to the alkali-silica reaction (ASR) and delayed ettringite formation (DEF) damage which affects real structures. In this paper, a parametric study is conducted to quantitatively study the effect of slight-to-severe ASR/DEF damage in the presence of stirrup confinement on the pullout behavior between concrete and reinforcement using three-dimensional rigid body spring model (3D RBSM) simulation. It is found through the simulation that the bond stress in ASR damaged cases increases when ASR expansion before pullout is small and then decreases as the damage level rises, while the bond stress in DEF damaged cases keeps decreasing from the beginning. Besides, higher stirrup confinement effectively mitigates bond deterioration in both ASR and DEF damaged cases when damage is serious. More importantly, stress development and crack propagation during the expansion stage and the pullout stage are visualized. Interface cracking condition varies according to the damage type (ASR or DEF) and the level of stirrup confinement due to different cracking mechanisms. However, the tendency for the number of cracks in the concrete to increase, which reflects the overall damage level in ASR and DEF damaged cases, is similar, resulting in a similar trend for bond stress to decrease.
Phenomenological process of rebar corrosion in reinforced concrete evaluated by acoustic emission and electrochemical noise
Yuma Kawasaki, Shinya Fukui, Tomoko Fukuyama
CONSTRUCTION AND BUILDING MATERIALS, Volume 352, 17 October 2022
(https://doi.org/10.1016/j.conbuildmat.2022.128829)
Abstract
Rebar corrosion was evaluated by monitoring reinforced concrete specimens. An electrical corrosion test accelerated the corrosion, and non-destructive evaluation of the acoustic emission (AE) and electrochemical noise (EN) was applied. Because AE phenomena were detected during rebar corrosion, the rise time and maximum amplitude increased, showing waveform variations. The AE activity was attributed to oxide film peeling of the rebar surface. The pitting index of the EN analysis ranged from –1 to 0, indicating localized corrosion. The EN method can detect pitting corrosion on rebar surfaces. AE and EN can be combined to phenomenologically evaluate early-stage rebar corrosion in concrete.
Mechanical behavior and models for porosity-free concrete reinforced with high amounts of steel fiber
Ryohei Yanagida, Takuro Nakamura, Katsuya Kono, Junichiro Niwa
CONSTRUCTION AND BUILDING MATERIALS, Volume 354, 7 November 2022
(https://doi.org/10.1016/j.conbuildmat.2022.129098)
Abstract
A new cementitious composite characterized by an extremely high compressive strength (>400 MPa), known as porosity-free concrete (PFC), has been recently developed. Many tests have been conducted to formulate appropriate stress–strain laws for compression and tension. This study clarified that PFC has extremely high compressive strength and post-cracking toughness owing to the reinforcing fibers. In addition, the flexural strength of porosity-free concrete was investigated by combining experimental and numerical analyses. Furthermore, the formulation of the stress–strain law in tension introduced ‚equivalent characteristic lengths” to convert the crack width into an equivalent strain.
Expansion characteristics of concrete with free lime based expansive additives under uniaxial restraint conditions
Mayank Gupta, Kolneath Pen, Go Igarashi, Yuya Takahashi, Tetsuya Ishida
CONSTRUCTION AND BUILDING MATERIALS, Volume 356, 21 November 2022
(https://doi.org/10.1016/j.conbuildmat.2022.129330)
Abstract
Expansive additives in higher dosages induce chemical prestress in concrete by imparting higher early-age expansion. However, induced stress and concrete expansion can vary significantly, depending on different restraint conditions. In addition, concrete expansion can be highly anisotropic depending on the nature of external restraints and boundary conditions. Experimentations have been performed to study the effect of uniaxial (anisotropic) restraint on the concrete expansion (in both restraint and stress-free directions) and induced prestress. A higher degree of restraint resulted in a substantial decrement in the longitudinal expansion. In contrast, expansion in the stress-free (lateral) direction was not much affected by the restraint in other direction. As a result, an overall decrement in the volumetric expansion was observed with an increase in the reinforcement ratios. Stress induced in concrete due to the restraint expansion in the longitudinal direction was found to be higher for a higher reinforcement ratio. Data provided from the current work can be used for the comprehensive modelling of expansive concrete under external restraints.
Experimental investigation on the mechanical and interfacial properties of fiber-reinforced geopolymer layer on the tension zone of normal concrete
Kazutaka Shirai, Junta Horii, Koki Nakamuta, Wee Teo
CONSTRUCTION AND BUILDING MATERIALS, Volume 360, 19 December 2022
(https://doi.org/10.1016/j.conbuildmat.2022.129568)
Abstract
This study aimed to understand the mechanical and interfacial properties of fiber-reinforced geopolymer (FRG) layer on the tension zone of normal concrete. A trial mix of FRG using local materials obtained in Hokkaido was investigated. Compression and splitting tensile tests on the FRG test pieces were conducted under different mixing procedures, constituents, volume fractions of the polyvinyl alcohol fiber, curing conditions, and ages. Flexural tests using FRG-normal strength concrete (NSC) composite specimens with different FRG layer thicknesses were carried out. By placing the FRG layer on the tension side of the composite specimen, the flexural strength and energy absorption were significantly increased. The flexural strength for the NSC alone was 3.5 MPa, while the FRG-NSC composite specimens showed higher flexural strengths of 6.1?6.6 MPa. Also, XRD, FTIR, and SEM analyses were carried out for the FRG samples.
Field investigation and finite element analysis on expansion and shrinkage strains of expansive concrete structures
Hakas Prayuda, Ganchai Tanapornraweekit, Somnuk Tangtermsirikul, Koji Matsumoto, Passarin Jongvisuttisune, Chalermwut Snguanyate
CONSTRUCTION AND BUILDING MATERIALS, Volume 360, 19 December 2022
(https://doi.org/10.1016/j.conbuildmat.2022.129598)
Abstract
This study investigated the strain behavior of various reinforced concrete structures cast with expansive concrete. Laboratory tests, field measurement, and finite element (FE) analysis on the expansion and shrinkage were investigated. Field measurement and numerical simulation were carried out on three different structures, i.e., slab on grade (SG), slab on beam (SB), and water tank wall (WT). Strain gauges are installed in several locations in each structure to study the effects of type and amount of expansive additive and restraining conditions on the level of expansion and shrinkage. To increase the flexibility and versatility of the design process, FE analysis is one of the comprehensive methods for estimating the expansion and shrinkage strain in expansive concrete structures under restraint. FE analysis in this study applies free expansion strain as an input, with the consideration of expansion loss due to pores filling of expansive products and early age compressive creep. The field measurement results indicated that the restraint (internal and external restraint) significantly affects the expansion and shrinkage strains in the structures. Furthermore, it was found that the application of effective free strain as the input in the FE analysis made it possible to predict the level of restrained expansion strain in expansive concrete structures. The expansion and shrinkage strains can be estimated accurately using the FE analysis by considering several factors such as degree of restraint, curing conditions, and mix proportions.
Investigating the hydration characteristics of a new composite cementitious binder containing of slag and calcite
Chuang Li, Siventhirarajah Krishnya, Masataka Ogino, Eiji Owaki, Yogarajah Elakneswaran
CONSTRUCTION AND BUILDING MATERIALS, Volume 361, 26 December 2022
(https://doi.org/10.1016/j.conbuildmat.2022.129629)
Abstract
The influence of the filler content, filler fineness and water to powder ratio (W/P) on hydration kinetics and microstructure behaviour of a new clinker-free material made of calcium hydroxide, blast furnace slag (BFS), calcite and expansive agent are explored in this study. The hydration characteristics of the proposed material were investigated by multiple experimental programmes including X-ray diffraction (XRD), TG-differential thermal analysis (DTA), selective dissolution measurement and mercury intrusion porosimetry (MIP). The experimental results revealed that slag reaction degree is enhanced by increasing the filler content and fineness of the filler in high W/P ratio. However, the filler fineness does not show significant improvement in the hydration degree of slag with low W/P ratio in later curing period due to the reduced amount of available water for the hydration reaction. Another interesting finding of this study is that the hemicarboaluminate which is thermodynamically unstable than monocarboaluminate, stably formed even at the later age of hydration reaction in the presence of calcium carbonate. The amended thermodynamic model also well agreed with the tendency of the experimental results in terms of hydration products and porosity of the hardened matrix as a function of curing period.