Concrete Overstrength: Assessment of Field Strength Seeking Insights for Overdesign Optimization

This study investigates the high contents of cementitious materials in Portland cement concrete and assesses the required (f’cr) and actual (σ) compressive strength of concrete specimens. A linear optimization technique identifies the required binder content to reach f’cr. Standard specifications have required concrete overdesign (OD) for decades, but few studies have evaluated the actual magnitude of OD from field data. The compressive strength of 958 cylinders prepared in the field represented 8200 m3 of ready-mixed concrete with 300 and 450 kg/m3 of cementitious are analyzed. The actual OD appears to be 7 to 21% higher than required. The required 28-day compressive strength of concrete was achieved in less than seven days. Therefore, the content of the cementitious materials could be reduced by 6 and 17% so that concrete could reach f’cr without cementitious overconsumption. Reducing cementitious content is recommended to improve construction quality and optimize resource utilization. Among the main reasons for this recommendation are the estimated substantial long-term savings, increased concrete durability and more rational use of natural resources required to build the structures.

NRG COSIA Carbon XPRIZE: carbon-dioxide mineralization in recycled concrete wash water

Wash water is generated as a waste stream from ready-mixed-concrete production. Reuse of the water as mixture water is limited, in practice, by the negative material performance impacts associated with the water chemistry and properties; the effects are intensified with increasing content of suspended solids and age. However, this waste material can be used as a beneficial additive to concrete by profiting from the cementitious properties of the suspended solids, if variability can be reduced. A method of stabilizing this material is through CO2 treatment. The added CO2 is mineralized through a reaction with the calcium from the cement particles. This provides a calcium-carbonate coating that prevents further cement hydration, making the material predictable. This has been shown to alleviate concerns with set acceleration and inconsistencies in compressive strength. A method of CO2 treatment was tested as part of the NRG COSIA Carbon XPRIZE at a site in Calgary, Alberta. The slurry for the treatment was provided by a local concrete plant and had a specific gravity of 1.15. The simulated wash water was treated in 1000-L quantities with each treatment mineralizing an average of 40 kg of CO2. The system ran for 1600 hours of operation over 127 treatment cycles and converted 14.5 tonnes of CO2 at an average mineralization efficiency of 80%. The treated slurry was used as an additive in >300 batches of concrete where the concrete met the necessary requirements for fresh properties and setting time, while achieving a strength benefit. Replacement of 5% and 10% of batch water with treated slurry (9.4 and 18.8 kg slurry/m3 concrete) showed a strength benefit of 3% and 6% compared to a reference. The technology was selected as the winner of the NRG COSIA Carbon XPRIZE (Track B: Natural Gas) in April 2021.

Design of High-Strength Concrete for Ready-Mixed Concrete Production

The high-strength concrete is a cement composite reaching high compressive strength, namely, pursuant to the legislation, higher than 60 MPa in the terms of cube compressive strength. The development of high-strength concretes exceeding 100 MPa is still an up-to-date issue and the production of these concretes is still limited only to a prefabrication. Contemporary construction industry and projecting activity have begun to focus on a construction of statically demanding buildings, which can include e.g. high-rise buildings. Such projecting often requires using of the state-of-the-art materials like cement composites with high mechanical parameters for construction of more subtle buildings. Within this article, the procedure of ready-mixed concretes development with the compressive strength around 100 MPa designed according to a project documentation for actual construction of high-rise building with the height up to 160 meters and 46 floors is described, together with the influence of the aggregate on the resulting composite strength.

Materials for 3D Concrete Printing: Approach to Standardization in Russia

3D Concrete Printing (3DCP) technology, compared to traditional monolithic construction, gives a possibility to increase the workspeed and reduce the manual laborproportion, reduce material consumption and also improve the architectural appearance of buildings being erected. At the same time, more stringent requirements are imposed on the material for 3D printing in terms of rheological characteristicscontrol, strength developmentkinetics, interplay adhesion and some other parameters than for conventional ready-mixed concrete. Therefore, to ensure the mass application of technologies for additive construction production using concrete as printing ink, it is necessary to develop a regulatory and technical base, including the development of standard test methods to determine the operational properties of this typeofmaterials. The article examines the main trends in the management of the materials’properties for construction 3D printing based on cement binders and describes the principles of building a system for standardizing materials for 3D printing construction in Russia, which was developed with the participation of the authors of this article.

Interlaboratory Comparative Tests in Ready-Mixed Concrete Quality Assessment

Proper quality assessment of ready-mixed concrete, which is currently the principal material for construction, land engineering and architecture, has an impact on the optimisation and verification of correct functioning of individual stages of the production process. According to the European Standard EN 206 “Concrete–Specification, performance, production and conformity”, obligatory conformity control of concrete is carried out by the producer during its production. In order to verify the quality of concrete, investors generally commission independent laboratory units to perform quality assessment of both concrete mix and hardened concrete, which guarantees a high quality of construction works. One of the essential tools for ensuring the quality of test results is the participation of laboratories in the so-called proficiency testing (PT) or inter-laboratory comparisons (ILC). Participation in PT/ILC programmes is, on the one hand, a tool for demonstrating the laboratory’s performance, on the other hand an aid for maintaining the quality of available concrete tests and validating test methods. Positive evaluation is a confirmation of the laboratory’s capability for performing the tests. The paper presents the results of laboratory proficiency tests carried out by means of inter-laboratory comparisons, as shown in the example of quality assessment of ready-mixed concrete for nine participating laboratories. The tests were performed for concrete of the following parameters: strength class C30/37, consistency S3, frost resistance degree F150, and water resistance degree W8. This involved determining consistencies, air content and density of the concrete mix, and compressive strength of hardened concrete. For the evaluation of laboratory performance results, z-score, ζ-score and En-score were applied. The innovation of the proposed study lies in employing both classical and iterative robust statistical methods. In comparison with classical statistical methods, robust methods ensure a smaller impact of outliers and other anomalies on the measurement results. Following the analyses, clear differences were found between the types of detected discrepancy of test results, which occurred due to the nature of individual parameters. For two laboratories, two scores revealed unsatisfactory results for concrete mix consistency. The main reasons can be pouring into the cone-shaped form a concrete mixture that is too dry, or incorrect use of a measuring tool also creating a possibility that the obtained value can be wrongly recorded. Other possible reasons are discussed in the paper. Participation in inter-laboratory comparison programmes is undoubtedly a way to verify and raise the quality of tests performed for concrete mix and hardened concrete, whereas individual analysis of the results allows the laboratory quality system to be improved.

A Method of Finding the Best Route and Shortest Route to a Ready Mixed Concrete Plant Through Real Time Tracking System by using GIS and GPS

The delay in transportation of ready mix concrete has become a common issue in civil engineering construction industry which wasted millions of rupees. This report is prepared as a part of the research conducted on developing a GIS based tracking system for truck mixers and a system to find the best route in transporting ready mixed concrete. Furthermore, it focuses on determining (VRP) feature in network analysis extension in ArcGIS. A shape files of road network in Colombo area was created using an open street map. The road network was mapped on the open street map shadflies using polylines. For this research, batching plant established in Colombo 14 and three construction sites in Kollupitiya and union place were considered. Relevant coordinates for both batching plant and the construction sites were imported to the map. Before caring out the final simulation, various constraints were assigned to ready mixed plants as well as for the routes such as one way restrictions etc. The traffic flow of the specific routes has been observed in two time frames such as normal peak hours (07:00 hrs. to 20:00hrs) and off peak hrs (20:00hrs to 7:00hrs). The main objective of this research is to developed an optimum delivery plan for truck mixers by using Arc GIS software and provide a guideline to develop this concept to be used in a much larger scale for beneficial of construction industry Keywords ArcGIS; ready mixed concrete; tracking system; Network planning