This study evaluates the performance of lightweight shotcrete incorporating municipal solid waste incineration bottom ash (MSWIBA) as both fine and coarse aggregates. A 50:50 mix of MSWIBA and standard sand was used as fine aggregate, while MSWIBA cold-bonded artificial lightweight aggregates (BALA) replaced natural coarse aggregates (NA) at 0-100 % volume ratios. Additionally, three types of lightweight aggregates-fly ash ceramsite (FAC), shale ceramsite (SC), and BALA-were compared at 100 % replacement level. A combined dosage of 6 % fly ash (FA) and 10 % silica fume (SF) was adopted to improve workability and bond strength. Results showed that the FA+SF system increased slump to 154 mm, reduced bleeding rate to 17.6 %, and enhanced bond strength by 26.4 %. Increasing BALA content improved flowability and 1-day strength (from 4.4 MPa to 25.5 MPa), while 28-day compressive and splitting tensile strengths declined. Among all artificial lightweight aggregate type, BALA-based concrete (BAC) showed the best balance between mechanical performance and sustainability, with a 28-day strength of 35.1 MPa. Compared to NA-based concrete (NAC), BAC reduced COQ emissions by 4.95 %, energy consumption by 0.63 %, and cost by 17.78 %. These findings demonstrate the feasibility of MSWIBA-based lightweight shotcrete for environmentally sustainable construction. The findings support the potential of MSWIBA-based aggregates in green construction applications and offer valuable reference data for practical engineering use.

The heat of hydration, mechanical properties, pozzolanic activity, and microscopic characteristics of cement pastes incorporating co-combusted fly ash (CCFA) were investigated, and the disparities between the CCFA/cement system and the coal fly ash (CFA) binding system were also compared. The results indicate a decrease in the heat of hydration for both CFA and CCFA samples, with a more pronounced trend observed as the fly ash content increased from 10% to 30%. The distinction in the early hydration between CFA and CCFA samples primarily manifested in the rate of heat release, potentially correlated with variations in the active Al2O3 content in the fly ash. Neither CFA nor CCFA samples exhibited significant cementitious activity at 3 days, functioning solely as inert fillers in the cement paste. By 3 and 28 days, the mechanical properties of both CFA and CCFA samples were inferior to those of pure cement paste. However, by 180 days of hydration, the compressive strength of CCFA-blended mortar notably increased, with the highest strength observed in the 10% CCFA-blended sample. Both CFA and CCFA samples produced the secondary hydration product C-A-S-H and demonstrated comparable consumption of calcium hydroxide (CH). These findings underscore the potential of CCFA as a supplementary cementitious material (SCM) and lay a foundation for its widespread adoption.

Ingress of chlorides (Cl-) in concrete structures is a resultant process under effects of various factors, in which stress distribution in concretes due to the external applied loads is of great importance but its impacts cannot be easily quantified via experiments. To further understand Cl- ingress in loaded concretes, a coupling numerical model considering different mechanical and transport properties of three concrete components (paste, aggregate and interfacial transition zone), heterogeneous distributed stress generated by axial loads and its resulted change in Cl- diffusion property and concrete microstructure is established. The model has been verified by lab based experiment results and can effectively reveal stress distribution, generation and propagation of cracks and Cl- related parameters in loaded concretes. The obtained results show that without considering the heterogeneous mechanical and transport properties of concrete components, ingress of Cl- in concretes will be underestimated, especially in those subjected to compressive or tensile loads of higher than 60% ultimate strength.

This study presents experimental and numerical investigations to comprehensively assess the impact of carbonation on the durability of chloride-blended seawater and sea-sand concrete. It reveals that carbonation leads to a reduction in pH and results in chloride redistribution along the carbonation depth. The microstructure of concrete after carbonation exhibits increased compaction, reduced porosity, and a refined pore structure. Rebar corrosion in this case is initiated by the excess of chloride ions, as proved by Raman results showing that corrosion product is composed of β-FeOOH. A mathematical model considering several affecting factors was proposed to predict the chloride redistribution in seawater and sea-sand concrete exposed to a carbonation environment, and the numerical results were fitted well with the experimental data. The initiation time for corrosion of the steel rebar is markedly shortened due to the combined effects of carbonation and chloride redistribution. It is verified that the ratio of is a key parameter in predicting corrosion initiation for chloride-blended concrete exposed to carbonation condition. The obtained results are expected to promote the resource utilization of seawater and sea-sand concrete in practical engineering.

The effects of pouring time intervals on the integrity of pulverized fuel ash (PFA) concrete were evaluated by measuring ultrasonic pulse velocity and compressive strength. Concrete was poured progressively at different time intervals (30 min, 45 min, and 60 min) under similar conditions after the first batch of concrete was vibrated. The effects of the water–cement ratio (w/c) on ultrasonic pulse velocity were also compared and analyzed. Both compressive strength and ultrasonic pulse velocity decreased as the pouring time interval increased. When the water–cement ratio was 0.55, the pouring time interval had little effect on compressive strength, but when the w/c was reduced to 0.45, improvements in the compressive strength of concrete with different pouring time intervals were as high as 10 MPa. Under the condition of the same w/c and the same pouring time interval, improvements in the compressive strength of the interface were as high as 15 MPa, and the prolongation of the aging period could reduce the difference in strength to 8 MPa. The formula Fc=0.63e0.95Vc was used to infer the compressive strength of fly ash concrete at different ages by ultrasonic pulse velocity.

Early-age creep of seawater sea sand concrete has a profound effect on construction engineering. This study investigates the ramifications of seawater and sea sand on the early-age creep behavior of concrete subjected to different compressive stresses. To discern the impact of seawater and sea sand on deformation, creep tests were conducted. In parallel, mechanical tests, shrinkage deformation tests, and capillary water absorption tests were conducted to elucidate the influence of seawater and sea sand on macroscopic performance. Moreover, mercury intrusion porosimetry and scanning electron microscopy were deployed to scrutinize the concrete's pore structure and microstructure. The findings reveal that seawater and sea sand precipitate augmented shrinkage and creep deformations in concrete, with seawater exerting a more pronounced effect. Furthermore, seawater and sea sand diminish the porosity of concrete, optimizing its pore structure by curtailing the count of large pores and augmenting the number of gel pores and capillary pores, thereby bolstering its durability. Seawater also reduces the critical stress threshold for the manifestation of nonlinear creep in early-age concrete, while sea sand exerts a minimal influence. These insights hold substantial implications for comprehending the influence of seawater and sea sand on the early-age creep of concrete and offer valuable guidance for their practical deployment in engineering projects.

Carbonation leads to decrease in chloride (Cl-) binding capacity of hardened cement paste, and subsequently endangers safety of reinforced concrete structures. During the research process, the results obtained by different standards and methods used to quantify the deterioration differ greatly and are unsuitable for comparison. To solve this issue, multiple standards, appointed with various conditioning regimes, for testing acid- and water-soluble Cl- contents in hardened cement paste were followed to evaluate binding capacity and stability of monosulfoaluminate (AFm) and tricalcium aluminate (C3AH6) on premixed Cl- exposed to external CO2. Results show that the methods used in three standards can completely dissolve the acid-soluble Cl-; the different conditioning temperatures lead to different water-soluble Cl- content measured, resulting in significance difference in the AFm chloride binding results, while the difference can be slight and negligible in the C3AH6. Cl- binding products of AFm was relatively stable within room temperature to 70 °C, and the stability decreased once higher than 70 °C; the products of C3AH6 showed relatively good stability between 20 and 100 °C. The Cl- binding capacity and stability of both AFm and C3AH6 were greatly reduced after a carbonation of 3 d. Detailed results for evaluating changes in the binding capacity of AFm before and after carbonation were related to the standards selected, while that for the C3AH6 was quite close.

Limestone Calcined Clay Cement (LC3) presents brilliant properties in binding Cl - so that the embedded steel bars are probably protected in Cl - -contaminated condition, which meets the need of sea sand application. However, the corrosion performance of steel bars embedded in LC3 paste with Cl - is unclear, especially in early age hydration. Thus, a series of experiments were carried out to evaluate the corrosion performance of steel bars on initial and hardened stages of hydration, including concentration of OH - and Cl - in real pore solution, open circuit potential (OCP) and chemical elements of steel bars. In terms of early age hydration, the OCP of steel bars and ions concentration in pore solution indicated that both specimens embedded in PC and LC3 pastes were at a highly corrosion state, however, elemental results showed that no obvious corrosion happened at this stage. With respect to hardened age hydration, visual corrosion could be seen on PC-embedded steel bars, with more Fe 3+ and O 2- , in comparison with LC3-embedded one, which was related to the much lower absolute OCP and Cl - concentration in pore solution. Overall, LC3 cement demonstrates protective effect on steel bar in special contaminated-Cl concentration.

This paper presents a new method for assessing the compositional changes of carbonated cement pastes subjected to high temperatures. In this new method, in-situ Raman mapping combined with X-ray photoelectron spectroscopy (XPS) was used to monitor the phase transformation in carbonated cement pastes subjected to various high temperatures from 30 to 950 degrees C. Two kinds of carbonated areas, i.e., vaterite dominated and calcite dominated, were found in the in-situ Raman measurements. With the elevation in temperature, most of the vaterite was converted to calcite at 500 degrees C and completely decomposed at 600 degrees C, while the decomposition of calcite started at 600 degrees C and finished at 720 degrees C. Meanwhile, the depolymerization of the calcium modified silica gel to the silicate phases with a lower degree of polymerization was initiated at 500 degrees C, which led to the crystallization of beta-C2S at 600 degrees C. The generation of beta-C2S was found to increase with the elevation in temperature and became the dominant phase at 950 degrees C. In conclusion, the high temperature could affect the stability of carbonated cement pastes at 500 degrees C and above. The in-situ Raman mapping measurement has provided an extraordinary view of the spatial distribution of interesting phases subjected to high temperatures in a nondestructive way, which should be more consistent with the true condition in the material.

The effects of temperature on the chloride-induced corrosion behavior of reinforcing steel in simulated sea-sand concrete pore solution are studied by means of linear polarization resistance. The results show that the Ecorr (corrosion potential) and icorr (corrosion current density) of the reinforcing steels are temperature and/or chloride concentration (CCl)-related parameters. A linear correlation between Ecorr and temperature and a natural logarithmic correlation between icorr and CCl are observed. It is proved that the relationship between the corrosion rate and temperature follows the Arrhenius equation, whereas the activation energy of corrosion reaction increases with the increase of CCl.

Microcapsule-based self-healing concrete was used in a tunnel engineering project in the Qianhai area, Shenzhen and the concrete performance was investigated using laboratory and field tests. The physical properties of the microcapsules and the microstructure of the self-healing concrete were experimentally investigated. The effects of the microcapsules on the strength, permeability, and long-term shrinkage of the self-healing concrete were also investigated. The self-healing efficiency was evaluated using a compressive strength test and a rapid chloride migration (RCM) test. The results indicated that the self healing functionality of the concrete containing 10% microcapsules gradually increased over time. The microcapsules had both positive and negative effects on the microstructure of the self-healing concrete. The use of the microcapsules resulted in a significant increase in the long-term shrinkage but the amount of shrinkage is acceptable for practical applications. No significant difference of the strain evolution was observed between the experimental and control groups in the field test, indicating that the use of microcapsule-based self-healing concrete is feasible and promising to improve the durability of concrete structures, especially in coastal civil engineering. (C) 2019 Elsevier Ltd. All rights reserved.

This paper presents the results of an experimental program investigating the behaviour of confined high strength concrete. Eighteen high strength concrete circular columns confined by spiral reinforcement were tested under axial compression. The test variables included concrete compression strength, the spacing of the spiral reinforcement and specimen height. The influence of the size of the effect on the behaviour of the confined concrete was investigated. Four confined concrete models which are defined in the literature were used to predict peak stress and strain of the core concrete (Mander et al., 1988; Fafitis & Shah, 1985; Razvi & Saatcioglu, 1999; Legeron & Paultre, 2003). A comparative study of the stress-strain model with the test results indicated that the models used in this study all produced a conservative prediction for the ductility of confined high strength concrete. The model proposed by Fafitis & Shah 1985 can make a more accurate prediction with standard deviation 3.92% and 21.88% in peak stress and strain, respectively, compared to predictions made by other models. (C) 2017 Elsevier Ltd. All rights reserved.

The influence of rebar locations on concrete conductivity at different ages is discussed.Combined with experiments,the relation of concrete conductivity,dielectric constant and concrete compressive strength is obtained,and the mathematical model between concrete compressive strength and dielectric parameter is established by Consensor system.Testing on site shows that the strength of cover concrete at early age can be obtained effectively with Consensor system.This is a rapid and convenient method for construction quality Control.

本文从土木工程专业工程测量实践教学的现状出发,就存在问题进行分析和探讨,结合实践教学改革成果,对工程测量实践教学所涉及教师队伍、实验条件、实践教学方式等内容进行了改革和探索,致力于提升土木工程测量实践教学效果.

In this article,concrete cracks and reinforcement corrosion emerge in pumping room and workshop of one coastal industry building after fifteen years using.According to field structural testing and environmental analysis,the main factor,which causes reinforcement corrosion,is due to construction quality of concrete protection layer.Because the engineer takes less consideration on chloride ion under coastal environment,the steel bar will be corroded widely as the thickness of concrete protection layer is less than the design value.As a result,the safety of reinforcement concrete structure is reduced.

某滨海建筑建成使用不到20年就呈现大面积钢筋腐蚀及混凝土胀裂,通过现场检测与分析,混凝土碳化深度过大以及混凝土中氯离子含量超标被认为是引起钢筋腐蚀的主要原因,且频繁干湿交替环境加剧了这一腐蚀过程。某滨海建筑建成使用不到20年就呈现大面积钢筋腐蚀及混凝土胀裂,通过现场检测与分析,混凝土碳化深度过大以及混凝土中氯离子含量超标被认为是引起钢筋腐蚀的主要原因,且频繁干湿交替环境加剧了这一腐蚀过程。

文章针对我国高校实验室管理存在的问题,围绕如何适应扩招后高校实验教学和人才培养的需要,结合本校实验室管理体制改革的实践,提出用发展的观点,促进产学研一体化,深化实验室管理体制改革,推动实验室上规模、上水平、上档次,建立教学科研相互结合、协调发展的实验室管理体制。