Documents published in Scipedia

• Carbonation-induced Early Corrosion Propagation Based Service Life Assessment Model (CECP-SAM)

  L. Chen, R. Su

  DBMC 2023.

  
  

  Abstract

  Supplementary cementitious materials (SCMs) are widely used for sustainable concrete. However, this is challenged due to the deteriorated resistance towards carbonation-induced corrosion. This paper introduces the establishment of a novel carbonation-induced early corrosion propagation based service life assessment model (CECP-SAM). This model is characterized by considering the early corrosion propagation (incipient cracking) and the use of supplementary cementitious materials. Based on experimental and numerical methods, the effects of binders, water/binder (W/B) ratio, exposure condition, cover thickness, rebar diameter, semi-carbonation zone, cathode-anode ratio on service life are investigated by CECP-SAM. The model is justified by using the results from a field investigation in Hong Kong. Performance-based service life equations are also given based on CECP-SAM.

  Abstract
  Supplementary cementitious materials (SCMs) are widely used for sustainable concrete. However, this is challenged due to the deteriorated resistance towards carbonation-induced [...]

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• Service Life Prediction of Concrete Against Freezing and Thawing Based on Water Absorption Results

  L. Xu, J. Wang, C. Zhang, Z. Li, Q. Yang

  DBMC 2023.

  
  

  Abstract

  Freezing and thawing resistance performance of concrete is a critical issue when evaluating the durability performance of concrete. This paper aims to predict the freezing and thawing resistance performance of concrete based water absorption indexes, meanwhile, five groups of experiments on porosity, short-term water absorption, long-term water absorption, MIP and pore structure scanning were respectively carried out for concrete. According to the experimental results, the important indexes such as porosity, water absorption, gas content and bubble spacing coefficient were obtained, which provided the basis for the prediction of durability and service life. The concept of equilibrium time ratio is introduced to simplify the calculation process. Based on the critical saturation theory, the service life of concrete against freezing and thawing is predicted by combining the environmental parameters and the indexes measured in experiments. The calculated results verified that the freeze-thaw durability life of air-entrained concrete is significantly increased compared with that of concrete without air-entrained concrete. In addition, a wide range of the service life was predicted for the 5 mixes, and the results could provide a guidance for selecting a proper mix design of concrete subjected to freezing and thawing.

  Abstract
  Freezing and thawing resistance performance of concrete is a critical issue when evaluating the durability performance of concrete. This paper aims to predict the freezing [...]

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• Microstructure of Cement Paste with Expansive Additives under Free and Restrained Conditions

  M. Gupta, G. Igarashi, Y. Takahashi, T. Ishida

  DBMC 2023.

  
  

  Abstract

  Expansive additives (EAs) have been widely used to reduce the risk of cracking due to shrinkage. Such additives cause early age expansion of concrete due to the formation of Portlandite and Ettringite in the pores of the cement paste, which affects the cement paste's microstructure. The presence of external restraints in the form of reinforcement and support affects the expansion and, ultimately the microstructure of cement paste. In the current study, the microstructure of cement paste with expansive additives is studied using mercury intrusion porosimetry (MIP). A free lime-based EA, with 10 and 15% (by weight) cement replacement ratios, is studied in the current study. The porosity and pore size distribution of the cement paste with EA were studied under free and restrained conditions. Results show that the under the stress-free condition, the porosity of the paste increased, while under the restrained condition, the porosity remained much similar to the reference case of OPC. Further, the pore size distribution of the cement paste with EA under free and restrained conditions is explained, and the effect of EA and restraint on the microstructure is discussed.

  Abstract
  Expansive additives (EAs) have been widely used to reduce the risk of cracking due to shrinkage. Such additives cause early age expansion of concrete due to the formation [...]

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• Study on Release Performance of Concrete Release Agent

  S. Lu, Z. Jie, W. Liya, Y. Maoqian, L. Tongwei

  DBMC 2023.

  
  

  Abstract

  In this paper, the effects of types of concrete release agent, the amount of brushing per unitarea and the 1d's strength of concrete on the release performance were studied. The adhesion and filmforming ability of O/W emulsion release agent was improved by adding high polymer. The results showthat the 1d's strength of concrete has no effect on the release performance of the release agent. The mostimportant factors affecting the release performance are brushing amount per unit area and the type ofrelease agent. O/W emulsion release agent with polyacrylamide and polyethylene glycol all stick mold. The more they are added, the heavier the stickiness is. While, the release performance with polyethyleneglycol is very close to blank sample.

  Abstract
  In this paper, the effects of types of concrete release agent, the amount of brushing per unitarea and the 1d's strength of concrete on the release performance were studied. [...]

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• Properties of Mineral Powders Modified Foamed Concrete

  Q. Liu, H. Chen

  DBMC 2023.

  
  

  Abstract

  In order to improve the stability of lightweight foamed concrete, the particle-stabilized foam (PSF) has been proposed because of its high stability. However, most PSFs added particles to foams, and few researchers have investigated whether the stabilization effect exists when particles are added to the paste. In this study, a new type of foamed concrete was prepared by adding different kinds of mineral powders to cement and using ionic surfactants to prepare foam. The influence of different mineral powders on the mechanical properties and durability of foamed concrete was investigated. Results showed that mineral powders decreased the drainage and disproportionation of foam, which stabilizes the foam. The excellent stability is attributed to the interaction between the mineral powders and ionic surfactants, which allows the mineral powders to adhere to the foam surface and form a dense granular film layer. Moreover, due to the interaction between mineral powders and ionic surfactants, hardened foamed concrete has a robust pore structure, which improves its properties.

  Abstract
  In order to improve the stability of lightweight foamed concrete, the particle-stabilized foam (PSF) has been proposed because of its high stability. However, most PSFs added [...]

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• Influence of Alkali-resistant Glass Fibers Distribution on Properties of Cementitious Composites

  B. Mrduljaš, A. Pranjić, M. Štefančić, K. Didulica, A. Baričević

  DBMC 2023.

  
  

  Abstract

  The waste hierarchy establishes a prioritized framework for effective waste management, where higher levels such as prevention, re-use, and recovery are associated with the conservation of primary resources and the retrieval of secondary resources. This approach aligns with the objectives of the construction industry, which aims to promote the efficient utilization of resources by treating raw materials in an environmentally responsible manner. In this context, utilizing waste fibers to reinforce cementitious composites becomes more logical than producing new fibers with similar properties. These waste fibers typically originate from the production of high-performance technical textiles used for structural repair and rehabilitation. By reusing these waste materials, the construction industry contributes a circular economy in its own sector and fosters cross-sectoral industrial symbiosis. Although the potential benefits and positive environmental impact of utilizing such materials are recognized, their influence on the properties of composites requires further investigation. This study examines the impact of production waste glass fibers on the properties of the mortar in both the fresh and hardened states. The study focusses on properties such as compressive strength and toughness. To gain a better understanding of the fibers’ contribution to the matrix properties, an investigation was conducted using µCT. The study focuses on investigating the effects of waste fibers with lengths of 5 and 10 mm and different dosages (0.2, 0.6 vol.%) on the properties of high-strength mortar, comparing them with factory fibers.

  Abstract
  The waste hierarchy establishes a prioritized framework for effective waste management, where higher levels such as prevention, re-use, and recovery are associated with the [...]

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• Study on Natural Passivation Behavior of Corrosion-resistant Steel Rebars in the Mortar

  G. Liu, D. Zhang, H. Chen, Z. Fan, Q. Wu

  DBMC 2023.

  
  

  Abstract

  The passivation behavior of HRB400 carbon steel rebar, 304 austenitic stainless steel rebar and 2304 austenitic-ferritic duplex stainless steel rebar during curing stage of mortar was studied by electrochemical testing techniques such as open-circuit potential, electrochemical impedance spectroscopy and linear polarization curve, and the corrosion resistance of the passivation film of the three rebars was compared to provide a reference for the practical engineering application of corrosion-resistant steel rebars. The study shows that all three types of steel rebars can be passivated during the 28 days curing stage of mortar, and 2304 duplex stainless steel rebars have the best passivation film corrosion resistance, followed by 304 stainless steel rebars, and HRB400 steel rebar was the worst.

  Abstract
  The passivation behavior of HRB400 carbon steel rebar, 304 austenitic stainless steel rebar and 2304 austenitic-ferritic duplex stainless steel rebar during curing stage of [...]

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• Property and Environment Evaluation of Cement Replaced with Treated Reclaimed Concrete Slurry Waste

  R. Jun, X. Yunqiu, L. Birunxuan, Z. Ji, L. Min

  DBMC 2023.

  
  

  Abstract

  The development of the cement industry consumes piles of natural resources and generating huge amount of waste and causing serious pollution, which can be partially solved by replacing with other cementitious materials, in particularly, solid waste. Reclaimed concrete slurry waste (RCSW), a corrosive and hazardous the residues from the reclaimed system for retrieving the aggregates from the returned concrete or cleaning the concrete mixer and trucks in the ready-mixed concrete plant, could that cannot be used to manufacture reclaimed concrete. However, the pre-hydration limits the hydraulic property of RCSW, which requires the proper treatment. This paper investigated the effect of three different treatment methods in improving the performance of RCSW and its feasibility of replacing cement under different substitution ratio in manufacturing reclaimed concrete. The treatment included sieving, shearing and ball-milling, and the substitution ratio was set as 15%, 30% and 45%, respectively. In addition to compressive strength and hydration properties, the environment impact of the cement paste replaced with RCSW were investigated as well. The results showed that compared within three methods, the shearing and ball-milling generated the treated RCSW with smaller particle size and high roundness. For the RCSW substituted cement paste, the substitution with 15% of treated RCSW provided the highest strength, meanwhile, while at a higher substitution ratio significantly reduced the compressive strength. The 15% of ball milling treated RCSW produced more products during the hydration process, resulting in a denser structure. According to the economic and environmental calculations, RCSW substitution reduced CO2 emissions, in which, the ball-milling method showed a lower carbon footprint.

  Abstract
  The development of the cement industry consumes piles of natural resources and generating huge amount of waste and causing serious pollution, which can be partially solved [...]

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• Oxygen Diffusion Property of Fatigue Damaged Concrete under Drying-wetting Cycle

  J. Zhilu, H. Sheng, F. Chuanqing, Y. Wenjie

  DBMC 2023.

  
  

  Abstract

  Oxygen diffusion has an important influence on the corrosion process of reinforced concrete structures. In the marine environment, concrete is subject to both fatigue loads and periodic drying-wetting conditions. In this study, the oxygen diffusion performance of damaged concrete due to fatigue is studied under drying-wetting cycle condition, which is of great significance to the development of concrete durability theory. The pore structures of concrete specimens with different damage degrees after drying-wetting cycle were measured by nuclear magnetic resonance (NMR). The effects of drying-wetting cycle and damage degree on pore structure were studied, and the oxygen diffusivity of damaged concrete before and after drying-wetting cycle was compared and analyzed. The results show that the pore size distribution curves of concrete specimens move to the smaller pores and the peaks decrease after 28 days of drying-wetting cycle. The proportion of gel pores (< 10 nm) increases and the proportion of medium and large capillary pores (10 - 1000 nm) decreases. After the drying-wetting cycle, the porosity of the damaged concrete specimens all decreased to certain degrees. It shows that the microstructure of the specimen is improved and the internal structure of concrete becomes more complex in the early stage of drying-wetting accelerated erosion. After the drying-wetting cycle, the oxygen diffusivity of all concrete specimens decreased, and the oxygen diffusivity of undamaged concrete decreased the most, about 10 times, but with the increase of damage degree, the reduction effect generally decreased.

  Abstract
  Oxygen diffusion has an important influence on the corrosion process of reinforced concrete structures. In the marine environment, concrete is subject to both fatigue loads [...]

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• Optimal Amorphous Oxide Ratios and Multifactor Models for Binary Geopolymers from Metakaolin Blended with Substantial Sugarcane Bagasse Ash

  L. Jing, T. Ye

  DBMC 2023.

  
  

  Abstract

  As a potential precursor, the utilization of sugarcane bagasse ash imparts enormous technical and environmental benefits to human society. However, its rich crystal content challenges the mix design of sugarcane bagasse ash-involved geopolymers. The present study is aimed to contribute toward the substantial utilization of sugarcane bagasse ash in geopolymers and develop a guideline for designing binary geopolymers from metakaolin and sugarcane bagasse ash. The experimental results show that when suitably designed, the compressive strength of metakaolin-sugarcane bagasse ash geopolymers satisfied the structural use in building engineering, and the sugarcane bagasse ash proportion could substantially reach up to 50%. Moreover, through a combination of mechanical, economic and environmental assessments, the optimal mixing proportions fall into the following ranges: SiO2/Al2O3=4.63~5.60, Na2O/Al2O3=1.5~2.0 and H2O/Na2O=8~10. Further, multi-factor models are proposed to regulate the mix design of binary geopolymers, with a R2 value beyond 0.9 .

  Abstract
  As a potential precursor, the utilization of sugarcane bagasse ash imparts enormous technical and environmental benefits to human society. However, its rich crystal content [...]

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