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H=Hyatt Regency Dallas; U=Union Station

Concrete with Recycled Materials, Part 1 of 2

Sunday, October 23, 2022  10:30 AM - 12:30 PM, H-Reunion C

The earth's natural resources are being consumed at a very high rate for many years. The potential depletion of resources, CO2 emissions and high energy consumption rates in the process of production, increase the necessity of recycling. All sectors of the society are responsible for these concerns, especially the construction industry. As a major construction material. concrete is increasingly judged by its environmental impacts and reusing the readily available concrete is becoming very important. Considering that much of the US infrastructures and urban buildings now require renovation and replacement, the concrete left behind can be a valuable source of aggregate for new concrete. Such concrete is usually called Recycled Aggregate Concrete. Through cost analyses, it is shown that using recycling concrete as aggregate for new concrete production can be a cost-effective method for construction.
Learning Objectives:
(1) Create public awareness of recycled concrete including its impact on reducing landfills and construction waste;
(2) Compare parameters of recycled aggregate concrete to natural aggregate concrete and evaluate the differences;
(3) Explain how recycled concrete can save natural resources and ecological environment leading to sustainable and greener world;
(4) Discuss the effect of adding different construction waste materials to concrete and the effect of this on recycled concrete properties.

This session has been AIA/ICC approved for 2 CEU/PDH credits.


Mortars with Recycled CO2

Presented By: Alessandro Fantilli
Affiliation: Polytechnic University of Turin
Description: Buildings and infrastructures can absorb CO2 from the atmosphere, because of the carbonation process that affects the calcium hydroxide of concrete elements. The aim of this research project is to initiate the absorption at casting, by adding dry ice pellets (made of recycled CO2) to cement-based mortars. Test results demonstrate that the flexural and compressive strength of the mortars are not modified by this addition. Conversely, due to the presence of CO2 , the standard deviation of strength reduces with respect to that measured in plain mortars. Thus, carbon dioxide can be considered a valuable resource that improves the mechanical behavior of construction materials.


A Ready-Mix Producers Method of Designing Recycle Concrete Aggregate Mix to be Used on the Job

Presented By: Frank Kozeliski
Affiliation: Koz. Consulting & Michele's Ready Mix, Rock & Recy
Description: This presentation will cover how one will design a mix using recycle concrete base and convert it into a concrete mix to develop the strength and be able to pump the mix. This concrete turns grey and gets hard with a few cracks. A real-life use of Recycle Aggregate Concrete.


Geometrical, Physical, Mechanical, and Compositional Characterization of Recycled Concrete Aggregates

Presented By: Jiong Hu
Affiliation: University of Nebraska-Lincoln
Description: While it is believed that recycled concrete aggregate (RCA) can be effectively incorporated into new concrete, its use is limited, mostly due to the absence of effective characterization of RCA. Current specifications and characterization methods mostly include only basic parameters such as specific gravity and absorption, which are not necessarily representing critical properties such as mechanical properties, residual mortar content, and freeze/thaw resistance. Through a recently completed ACI CRC project, this study included a set of different test methods to evaluate RCA collected from various sources. Test methods to identify aggregate crushing value and residual mortar content were modified to accurately characterize a variety of RCA without excessive variability introduced by human factors. The freeze-thaw resistance test with a modified data analysis protocol proved to be capable of differentiating the level of air-entrainment of parent concrete. Aggregate shape and texture were shown to significantly impact the void content of an aggregate granular matrix. A better understanding of RCA physical, mechanical, and compositional properties was achieved, which is critical in designing new concrete and evaluating the effect of RCA on new concrete.


Developing Class C Fly Ash Based Alkali-Activated 3D-Printed Concrete Mixtures

Presented By: Mohamed ElGawady
Affiliation: Missouri S&T
Description: This study investigated the use of class C fly ash (FA) as a precursor for alkali activated mortar (AAM) for 3D-printed concrete (3DPC). AAMs with different water to FA (W/FA), alkaline activator to FA (Alk/FA), and sodium silicate to sodium hydroxide (SS/SH) ratios were examined to achieve mixtures that can be tailored for different structural applications of 3DPC. The fresh properties including extrudability and buildability were evaluated through the open time (OT) and immediate deformation tests, respectively. Different cycle times (CTs) were applied to achieve a strain limit state necessary to maintain the printed shape. The strength of AAMs in different directions at different CTs was examined. Scanning electron microscopy (SEM) was carried out on AAM specimens having different CTs for a better understanding of the bond area. OTs ranging from 2.5 minutes to 31 minutes and axial strains ranging from 0.17 to 11% were achieved depending on the proportions of the AAMs and CT, which offers flexibility in optimizing the speed of printing and strength of concrete for different projects. The 3DPC specimens displayed anisotropic behavior compared to full-height specimens, where the compressive strength of full-height specimens was higher by 0.2-18% and 0.9-28% than 3DPC specimens tested parallel and normal to the printing directions, respectively. SEM images and line scan indicated approximately an even intensity of the element concentration at the interfacial zones of AAMs having short CT which explained the relatively high compressive strength of those specimens. While for AAM having long CT, there was a significant change in the intensity of the element concentration at the interfacial bond zone, and voids were observed resulting in low compressive strength of those specimens.


Mechanical and Durability Performance of Recycled Tire Steel Fiber Reinforced Concrete

Presented By: Qingli Dai
Affiliation: Michigan Technological University
Description: Recycled tire steel fibers (RSF) can be potentially utilized in cement concrete to improve its mechanical performance. However, due to the recycling process, RSF from different sources showed many differences in fiber length and aspect ratio. This study's objective is to evaluate the mechanical and durability performance of concrete with two types of RSF (long-thick fibers and short-thin fibers) and to optimize their fiber content for use in concrete. The RSF was added with the percentages of 0.5% and 1.0% by the mix volume. The plain concrete samples, reinforced concrete samples with different types and percentages of RSF were prepared. The compressive and indirect tensile strength were measured and compared. The fracture strength and fracture energy were measured with the single-edge notched beam test to evaluate the effects of different types of RSF. The freeze-thaw resistance tests and permeability tests were conducted to evaluate the durability performance of these sample types. These results can facilitate the recycling of different tire steel fibers while maintaining or improving the mechanical and durability performance of concrete.


The Influence of Biomass Fly Ash on the Rheology and Pozzolanic Properties of Portland Limestone Cement Paste

Presented By: Ahmed Ibrahim
Affiliation: University of Idaho
Description: Efforts have been geared in recent time on the possibility of using agro-allied industry waste in concrete, with the goal of achieving a cleaner environment and environmentally friendly construction. Biomass fly ash (BFA) and limestone clinker are waste from steam/power plants and the cement industry, respectively, and are of high relevance to economic and environmental problems. The influence of biomass fly ash on the rheology and pozzolanic properties of Portland limestone cement (PLC) pastes are presented. The BFA was used as partial replacement for PLC as supplementary cementitious materials (SCMs). The rheological properties (yield stress, viscosity and thixotropy) of the cement paste were determined using a parallel-plate rotational rheometer. The pozzolanic properties were determined using thermogravimetric analysis (TGA) by measuring the amount of calcium hydroxide (CH), and calcium silicate hydrate (CSH) of the hydrated paste, as well as the reaction kinetics. Different characterization techniques including X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy (SEM) were used to study the microstructure and mineralogy of the BFA. It was observed that the mineral composition of the biomass fly ash is like class C fly ash. At 15% of cement replacement the paste exhibits better rheological properties: lower yield stress and lower viscosity up till 120 min. after mixing, which is an important factor in ready-mix concrete plants. However, a better pozzolanic behavior was observed at 20% cement replacement. From the results obtained, the properties of the paste containing BFA is very sensitive to water/binder ratio (w/b). Above 20% cement replacement, it is suggested to use viscosity modifying agent (VMA) to get a better rheology and pozzolanic behavior.


Mechanical Properties and Cracking Potential of Portland Cement Based- and Alkali-Activated Materials Containing Waste Glass Powder

Presented By: Mehrab Nodehi
Affiliation: Texas State University San Marcos
Description: In the construction industry, the production, processing, and transportation of ordinary portland cement (OPC) is a significant contributor of greenhouse gas emissions. Harvesting raw materials (e.g., limestone) for the cement production can lead to natural resource depletion. To mitigate the negative impacts of OPC and improve concrete performance, supplementary cementitious materials (SCMs) have been used for decades. However, the projected reduction in the availability of traditional SCMs, such as coal fly ash, has increased the interest in searching for alternative and widely available SCMs. One of such materials is glass that has an annual production of around 100 million tons, but due to the high energy consumption in recycling glass, the glass industry has a low recycling rate (about 26%). The use of ground waste glass as a SCM can have substantial energy and economic implications due to the reduction in landfilling of this waste material. In this study, the mechanical properties and cracking potential of traditional portland cement based- and alkali-activated materials containing waste glass powder were investigated via a series of mechanical tests and a customized ring test. The results showed that the aluminosilicate-based glass powder performed very differently in the two binding systems. In addition, the ring test showed that the cracking time, pattern, and width are significantly different between the two binding systems.


Mechanical Properties and Cracking Potential of Portland Cement Based- and Alkali-Activated Materials Containing Waste Glass Powder

Presented By: Xijun Shi
Affiliation: Texas State University
Description: In the construction industry, the production, processing, and transportation of ordinary portland cement (OPC) is a significant contributor of greenhouse gas emissions. Harvesting raw materials (e.g., limestone) for the cement production can lead to natural resource depletion. To mitigate the negative impacts of OPC and improve concrete performance, supplementary cementitious materials (SCMs) have been used for decades. However, the projected reduction in the availability of traditional SCMs, such as coal fly ash, has increased the interest in searching for alternatively and widely available SCMs. One such materials is glass that has an annual production of around 100 million tons, but due to the high energy consumption in recycling glass, the glass industry has a low recycling rate (about 26%). The use of ground waste glass as a SCM can have substantial energy and economic implications due to the reduction in landfilling of this waste material. In this study, the mechanical properties and cracking potential of traditional portland cement based- and alkali-activated materials containing waste glass powder were investigated via a series of mechanical tests and a customized ring test. The results showed that the aluminosilicate-based glass powder performed very differently in the two binding systems. In addition, the ring test showed that the cracking time, pattern, and width are significantly different between the two binding systems.


Field Application of Cement-free Geopolymer Concrete using Fly Ash, Slag, or Red Mud with Optimized Cost and Performances

Presented By: Lin Shen
Affiliation: University of Hawaii at Manoa
Description: Finding a sustainable alternative to cement is crucial to mitigate climate change. This presentation introduces an innovative approach to investigate alkali-activated binders and monitor kinetic reaction using Raman spectroscopy. The dissolution of precursors by alkalis was continuously monitored for 24 hours immediately after mixing, which was found to be especially helpful to optimize the appropriate mixing procedure. Coupled with a new method for predicting the final products of alkali-activated materials using comprehensive phase-analysis, the cost and performances could be better controlled and optimized. Field applications of optimized AAM mixes based on fly ash, slag, or red mud could achieve 1) cement free with more than 80% reduction in carbon footprint, 2) ~25% reduction in cost, 3) cured at ambient temperature with well controlled setting time, flowability and other fresh properties, 4) similar or even superior hardened properties and durability, and 5) mass production ready.

Upper Level Sponsors

Ash Grove
Baker
Conseal
Controls Group
Euclid Chemical
GCP
Master Builders
PoreShield
PS=0
ACI Northeast Texas Chapter

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