Analysis of a Composite Admixture Based on Ready-Mixed Concrete Waste Residuals

Reasonable treatment and utilization of waste residuals discharged during the production of ready-mixed concrete is an important problem in the cement industry.In this study,a composite admixture was prepared by using ready-mixed concrete waste residuals,furnace slag,and water granulated slag.The grinding characteristics of such material were investigated.Moreover,the effect of such admixture on cement hydration and pore structure was analyzed by X-ray diffraction,thermogravimetric-differential scanning calorimetry,scanning electron microcopy and mercury intrusion porosimetry.As shown by the results:The grinding characteristics of the waste residuals can be improved significantly by mixing them with furnace slag and water granulated slag.Furthermore,the composite admixture does not change the composition of hydration products;rather it contributes to refine the pore structure of the matrix,thus improving the mechanical properties of these cement-based materials.

Effects of Sand Quality on Compressive Strength of Concrete: A Case of Nairobi County and Its Environs, Kenya

Failure of concrete structures leading to collapse of buildings has initiated various researches on the quality of construction materials. Collapse of buildings resulting to injuries, loss of lives and investments has been largely attributed to use of poor quality concrete ingredients. Information on the effect of silt and clay content and organic impurities present in building sand being supplied in Nairobi County and its environs as well as their effect to the compressive strength of concrete was lacking. The objective of this research was to establish level of silt, clay and organic impurities present in building sand and its effect on compressive strength of concrete. This paper presents the findings on the quality of building sand as sourced from eight supply points in Nairobi County and its environs and the effects of these sand impurities to the compressive strength of concrete. 27 sand samples were tested for silt and clay contents and organic impurities in accordance with BS 882 and ASTM C40 respectively after which 13 sand samples with varying level of impurities were selected for casting of concrete cubes. 150 mm × 150 mm × 150 mm concrete cubes were cast using concrete mix of 1:1.5:3:0.57 (cement:sand:coarse aggregates:water) and were tested for compressive strength at the age of 7, 14 and 28 days. The investigation used cement, coarse aggregates (crushed stones) and water of similar characteristics while sand used had varying levels of impurities and particle shapes and texture. The results of the investigations showed that 86.2% of the sand samples tested exceeded the allowable limit of silt and clay content while 77% exceeded the organic content limit. The level of silt and clay content ranged from 42% to 3.3% for while organic impurities ranged from 0.029 to 0.738 photometric ohms for the unwashed sand samples. With regard to compressive strength, 38% of the concrete cubes made from sand with varying sand impurities failed to meet the design strength of 25 Mpa at the age of 28 days. A combined regression equation of with R2 = 0.444 was generated predicting compressive strength varying levels of silt and clay impurities (SCI), and organic impurities (ORG) in sand. This implies that 44% of concrete’s compressive strength is contributed by combination of silt and clay content and organic impurities in sand. Other factors such as particle shapes, texture, workability and mode of sand formation also play a key role in determination of concrete strength. It is concluded that sand found in Nairobi County and its environs contain silt and clay content and organic impurities that exceed the allowable limits and these impurities result in significant reduction in concrete’s compressive strength. It is recommended that the concrete design mix should always consider the strength reduction due to presence of these impurities to ensure that target strength of the resultant concrete is achieved. Formulation of policies governing monitoring of quality of building sand in Kenya and other developed countries is recommended.

Reliable evaluation method of quality control for compressive strength of concrete

Concrete in reinforced concrete structure (RC) is generally under significant compressive stress load. To guarantee required quality and ductility, various tests have to be conducted to measure the concrete’s compressive strength based on ACI (American Concrete Institute) code. Investigations of recent devastating collapses of structures around the world showed that some of the collapses directly resulted from the poor quality of the concrete. The lesson learned from these tragedies is that guaranteeing high quality of concrete is one of the most important factors ensuring the safety of the reinforced concrete structure. In order to ensure high quality of concrete, a new method for analyzing and evaluating the concrete production process is called for. In this paper, the indices of fit and stable degree are proposed as basis to evaluate the fitness and stability of concrete’s compressive strength. These two indices are combined to define and evaluate the quality index of the compressive strength of concrete. Prin-ciples of statistics are used to derive the best estimators of these indices. Based on the outcome of the study, a concrete compres-sive strength quality control chart is proposed as a tool to help the evaluation process. Finally, a new evaluation procedure to assess the quality control capability of the individual concrete manufacturer is also proposed.

Analysis and interpretation on the concrete quality of shaft lining by elastic wave technique

The quality problem of the concrete body and backwall grouting of shaft lining must be taken into consideration during the engineering construction of the shaft. Detection and evaluation are needed to determine the parameters such as the location and depth of drilling. The record of elastic wave can be gained through laying the surveying lines of the ring and ver- tical direction in the shaft lining by the elastic wave method. And specifically, through analyzing the different parameters of seismic attribute such as the velocity of high frequency reflection wave, amplitude and frequency, the abnormal range on the wall or under the wall can be forecasted. The concrete quality of shallow layer in the shaft lining can be evaluated through the velocity of surfer wave. Using the evaluating technique of comprehensive frequency and the phase feature of waveform, the basic features such as inner construction, wall back filling and failure depth of shaft lining can be interpreted from qualitatively to half quantitatively, and the interpreting section can be drawn. The results show that the detection effect for the shaft quality is significant by elastic wave technique, and the delineation of abnormal areas is accurate. Its guidance function is better for pro- duction.

Analysis on Construction Quality Control Technology of Reinforced Concrete Shear Wall Structure

In the process of continuous development of construction enterprises, new requirements have been put forward for construction projects. By strengthening the construction quality control of reinforced concrete shear wall structure, the construction level of reinforced concrete can be continuously improved, the construction quality can be guaranteed, and the construction project can be successfully completed, which is worthy of extensive application and promotion in construction enterprises, thus providing a broader development space for construction enterprises.

Study on Quality Control of Concrete Raw Materials in Road and Bridge Construction

The main material of concrete is a construction building material composed of water and mineral mixture and cement and chemical additives in the corresponding proportion and below the standard.In the process of making concrete material,slurry and cement are needed to mix,then cement slurry and sand are mixed into mortar according to the corresponding proportion,and aggregate is added to mortar to form concrete building material.In the process of concrete preparation,the most important construction link is mixing,which needs to be fully stirred to make the performance of concrete meet the construction needs.In the process of concrete construction technology development,both mix ratio and production technology have become more and more mature,but there are still some problems,which have an impact on the quality of concrete[1].Therefore,this paper discusses the quality control of concrete raw materials according to the construction process of road and bridge.

Study on Food-making Quality of Strong-gluten Wheat Varieties from Lime Concretion Black Soil Area in the Huanghuai Wheat Region

In this study, 13 strong-gluten wheat varieties screened by the Key Project of Modern Agricultural Industry Technology System ＂Study on Industrial Technology for Strong-gluten Wheat from Lime Concretion Black Soil Area in the Huanghuai Wheat Region＂ were used as experimental materials to investigate their bread-making quality, noodle-making quality and other related characteristics. The results showed that more than half of the wheat varieties had better bread-making quality; the bread made from wheat with longer dough mixing time than 3.0 min had better texture, lighter color, and better taste. All these 13 strong-gluten wheat varieties showed good noodle-making quality in color, appearance, smoothness and taste; the differences between varieties were mainly found in palatability and viscoelasticity. Jimai 20, Xinong 979, Zhengmai 7698, Ji＇nan 17 and Zhengmai 9023 exhibited excellent bread-making quality; Zhengmai 366, Jimai 20 and Xinong 979 displayed excellent noodle-making quality. Fresh dough sheets made from Zhengmai 366, Jimai 20 and Xinong 979 exhibited slight color variation within 24 h and high peak starch paste viscosity; dry and cooked noodles made from Zhengmai 366, Jimai 20 and Xinong 979 had good quality.

Auto Identification of Rolling Layers in Roller-Compacted Concrete Dam

A scheme for identifying rolling layers in roller-compacted concrete (RCC) dam automatically was presented. First, a conceptual model was developed. Second, by using a computational geometry method, the auto identification of rolling layers and auto matching between rolling compaction machines and rolling layers were realized based on spatial control points. An application to the construction of Guandi RCC dam showed that the auto identification of rolling layers played an important role in ensuring the engineering quality.

Deep Learning-Based Automatic Detection and Evaluation on Concrete Surface Bugholes

Concrete exterior quality is one of the important metrics in evaluating construction project quality.Among the defects affecting concrete exterior quality,bughole is one of the most common imperfections,thus detecting concrete bughole accurately is significant for improving concrete exterior quality and consequently the quality of the whole project.This paper presents a deep learning-based method for detecting concrete surface bugholes in a more objective and automatic way.The bugholes are identified in concrete surface images by Mask R-CNN.An evaluation metric is developed to indicate the scale of concrete bughole.The proposed approach can detect bugholes in an instance level automatically and output the mask of each bughole,based on which the bughole area ratio is automatically calculated and the quality grade of the concrete surfaces is assessed.For demonstration,a total of 273 raw concrete surface images taken by mobile phone cameras are collected as a dataset.The test results show that the average precision(AP)of bughole masks is 90.8%.

Method of effective evaluation for examination of chloride ion in concrete

The chloride ion contained in reinforced concrete seriously corrodes the steel surface and damages concrete, resulting in inferior reinforced concrete that strength seriously compromises the entire structure’s safety. Consequently, the examination of chloride ions contained in reinforced concrete becomes an important part of a complete quality control procedure. To effectively check the concentration of chloride ions in concrete, the evaluation process should be accurate and precise. Laboratory data ob- tained using existing evaluation methods for the examination of chloride ion are not sufficiently objective to yield reliable results with accuracy and consistency for each sample. An evaluation algorithm with capability to define indices of precision degree (Ep) and accuracy degree (Ea) is presented in this paper. The authors established a statistically reliable index of unbiased estimators and equations to critically examine the laboratory methods’ precision, accuracy degrees and application value for measuring chlorine ion concentration in reinforced concrete.

Research Progress of Eco-Friendly Portland Cement Porous Concrete:A Review

With the great impetus of energy conservation and emission reduction policies in various countries,the proposal of concepts such as“Sponge City”and“Eco-City”,and the emphasis on restoration and governance of ecological environment day by day,portland cement porous concrete(PCPC),as a novel building material,has attracted more and more attention from scientific researchers and engineers.PCPC possesses the peculiar pore structure,which owns numerous functions like river embankment protection,vegetation greening as well as air-cleaning,and has been of wide application in different engineering fields.This paper reviews the salient properties of PCPC,detailedly expounds the research progress of domestic and foreign literature about this subject in the past ten years(2010–2020),conducts the statistical analysis of the distribution rule of its major properties around the world,combines with the engineering application to summarize the excellent properties of PCPC,and makes a forecast of future research direction.

Intelligent compaction theory of high roller compacted concrete dam

The concept and realization process of intelligent compaction for the construction of high roller compacted concrete dam were presented, as well as the theory of monitoring and intelligent feedback control. Based on the real-time analysis of the compaction index, a multiple regression model of the dam compactness was established and a realime estimation method of compaction quality for the entire work area of roller compacted concrete dam was proposed finally. The adaptive adjustment of the roiling process parameters was achieved, with the speed, the exciting force, the roller pass and the compaction thickness meeting the standards during the whole construction process. As a result, the compaction quality and construction efficiency can be improved. The research provides a new way for the construction quality control of roller compacted concrete dam.

Comparative Analysis of PM10 Emission Rates from Controlled and Uncontrolled Cement Silos in Concrete Batching Facilities

This research study quantifies the PM10 emission rates (g/s) from cement silos in 25 concrete batching facilities for both controlled and uncontrolled scenarios by applying the USEPA AP-42 guidelines step-by-step approach. The study focuses on evaluating the potential environmental impact of cement dust fugitive emissions from 176 cement silos located in 25 concrete batching facilities in the M35 Mussafah industrial area of Abu Dhabi, UAE. Emission factors are crucial for quantifying the PM10 emission rates (g/s) that support developing source-specific emission estimates for areawide inventories to identify major sources of pollution that provide screening sources for compliance monitoring and air dispersion modeling. This requires data to be collected involves information on production, raw material usage, energy consumption, and process-related details, this was obtained using various methods, including field visits, surveys, and interviews with facility representatives to calculate emission rates accurately. Statistical analysis was conducted on cement consumption and emission rates for controlled and uncontrolled sources of the targeted facilities. The data shows that the average cement consumption among the facilities is approximately 88,160 (MT/yr), with a wide range of variation depending on the facility size and production rate. The emission rates from controlled sources have an average of 4.752E-04 (g/s), while the rates from uncontrolled sources average 0.6716 (g/s). The analysis shows a significant statistical relationship (p < 0.05) and perfect positive correlation (r = 1) between cement consumption and emission rates, indicating that as cement consumption increases, emission rates tend to increase as well. Furthermore, comparing the emission rates from controlled and uncontrolled scenarios. The data showed a significant difference between the two scenarios, highlighting the effectiveness of control measures in reducing PM10 emissions. The study’s findings provide insights into the impact of cement silo emissions on air quality and the importance of implementing control measures in concrete batching facilities. The comparative analysis contributes to understanding emission sources and supports the development of pollution control strategies in the Ready-Mix industry.

Seepage Mitigation in Hydropower Dams by Optimization in Roller Compacted Concrete Interlayer (Monoliths) Joint Bonding Technology

Roller Compacted Concrete (RCC) has gained favorable recognition in hydropower and water resource dam construction. With optimization in construction technology and materials used for RCC Dams, cost is no longer a major disadvantage as compared to environmental impact, that is, wildlife habitat disruption. In as much as it has become optimal for investment in hydropower dam construction, the scourge for dam failure is still eminent, which is as a result of excessive seepage compromising the integrity of the mechanical properties of the dam. The aim of the paper is to highlight successful application methods in joint bonding to avoid excessive seepage and reduce the autogenous healing to a few years of operation. In view of optimization, this paper presents a comprehensive study on the influences of interlayer joints bonding quality from RCC mix performances and how it consolidates the RCC layers to withstand the shear strength along the interface, especially on the high dams. The case study is the RCC dam at the 750 MW Kafue Gorge Lower Hydropower Station. The scope of the study reviews the joint type judged by Modified Maturity Factor (MMF) with joint surface long time exposed in regions with dry and high temperature, technical measures of layer bonding quality control under condition of long time joint surface exposure, effects of joints shear strength and impermeability of the RCC layers when under the conditions of plastic and elasticity. The subtle observations made during the dam construction phases were with respect to the optimal use of materials in relation to RCC mix designs and the basis for equipment calibration for monitoring important data that can be referenced during analysis of shear forces acting on the RCC dam over time.

Geometric quality evaluation of three-dimensional printable concrete using computational fluid dynamics

The importance of geometrical control of three dimensional(3D)printable concrete without the support of formwork is widely acknowledged.In this study,a numerical model based on computational fluid dynamics was developed to evaluate the geometrical quality of a 3D printed layer.The numerical results were compared,using image analysis,with physical cross-sectional sawn samples.The influence of printing parameters(printing speed,nozzle height,and nozzle diameter)and the rheological behavior of printed materials(yield stress),on the geometrical quality of one printed layer was investigated.In addition,the yield zone of the printed layer was analyzed,giving insights on the critical factors for geometrical control in 3D concrete printing.Results indicated that the developed model can precisely describe the extrusion process,as well as the cross-sectional quality.

UHPC湿接缝浇筑的质量控制技术研究

污水处理厂生物反应池预制拼装施工复杂,超高性能混凝土(UHPC)湿接缝连接部位施工不当可能产生裂缝。结合工程实例,针对现场施工空间受限、湿接缝浇筑长度超过25 m等难点,采用UHPC搅拌泵送智能化一体机、分段连续浇筑、分阶段多重养护等措施,确保了UHPC湿接缝浇筑施工的顺利进行,有效解决了超长湿接缝开裂风险,提升了湿接缝浇筑质量。

混凝土施工技术在路桥施工中的应用研究

随着经济社会的快速发展,人们的生活水平越来越高,各种产业蓬勃发展。混凝土技术是工程施工过程中的一项重要技术,在路桥工程中的应用对提高工程质量具有重要价值。因此,从研究混凝土施工技术的特点入手,分析混凝土施工技术在混凝土中的应用,并结合实际施工分析其控制难点,旨在促进混凝土施工技术的有效应用,切实提高路桥工程质量。

机场道面装配式修复技术研究综述

为明确装配式水泥混凝土道面的技术特点,便于机场道面修复的技术选型,开展了文献调研,总结典型的装配式道面结构组合和接缝设计,梳理施工质量控制和数字化管控技术,并与其他道面修复技术在适配荷载、使用寿命和施工效率等指标进行对比分析。调研结果表明,钢筋环焊接的接缝设计具备施工简便的优势,预应力连接和可拆装传力构件能分别提升道面的抗弯拉性能和可复用能力,采用切割机、起吊钢梁和起吊调平一体化构件等装置可以提升施工作业效率。在道面修复的应用场景中,装配式混凝土道面适用于长期重型荷载,并在大面积修复作业中具有优势,可与快修混凝土材料配合作业,提升机场道面的韧性恢复能力。

碾压混凝土分层碾压离散元模拟及施工成层细观机理研究

碾压混凝土(RCC)坝特有的大仓面分层碾压工艺带来的层间结合质量问题,是影响其安全运行的重要因素。从施工控制的角度分析RCC施工成层机理,进而合理调整碾压参数,可有效保证大坝的施工质量。首先,通过RCC分层碾压试验,分析了碾压过程中含层面RCC的沉降规律、压实度及抗剪强度,为后续离散元模拟提供了基础;然后,建立并验证了RCC双层碾压与抗剪试验离散元模型;最后,给出了表征层间结合质量的骨料嵌入值指标,进而从孔隙率、层间骨料嵌入、层面应力分布、层间抗剪强度等方面分析了RCC施工成层的细观机理。结果表明:碾压参数对RCC的嵌入值、压实特性、层面应力和层间结合质量均有一定影响;嵌入值是影响层间抗剪强度的重要因素,二者呈线性相关,嵌入值每增加1 mm,模拟抗剪强度约增加1.583 MPa;激振力的增加以及行进速度、碾压厚度的减小均有利于提高层间结合质量,且碾压厚度是影响层间结合质量的最敏感参数。研究结果可为施工中RCC层间结合质量控制标准的制定提供理论依据。

基于SNA的装配式混凝土建筑质量影响因素分析

近几年,我国开始大力推行装配式混凝土建筑,但质量问题却难以突破。基于此,通过大量文献研究和专家访谈,识别出影响装配式混凝土建筑质量的因素,运用社会网络分析法,分析各影响因素之间的关联性,找出关键因素,并针对关键影响因素提出了相应的质量保证措施。