Concrete is the world’s most widely used construction material. Yet, the production of portland cement, an essential constituent of concrete, leads to greenhouse gas emissions into the atmosphere. The production of 1 ton of portland cement clinker releases approximately one ton of CO2 and other greenhouse gases. Environmental considerations have been a major thrust for the sustainable development of the cement and concrete industries. A sustainable concrete structure is designed and built to have a positive environmental footprint during its entire life cycle. Concrete is increasingly being considered as a sustainable material owing to its low inherent energy requirements and little associated waste. Not only is it made from some of the most plentiful resources on Earth, it can also be made with numerous recycled materials and by products and is itself entirely recyclable. Emerging breakthroughs in concrete technology have allowed the production of ultra high performance concrete requiring fewer raw materials, along with structures that are much more durable to reduce maintenance, repair, and reconstruction.
(1) Reduce the use of new virgin aggregate to save the environmental costs;
(2) Eliminate the use of landfills by reusing valuable materials that can be recovered and redeployed;
(3) Save the energy required for producing new concrete from raw materials and all associated costs;
(4) Conserve the natural resources for future use.
This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.
Impact of Recycled Concrete Aggregate Parent Concrete Strength on Mechanical Properties of Recycled Aggregate Concrete
Presented By: Noah Thibodeaux
Affiliation: New Jersey Institute of Technology
Description: Construction and demolition activities account for a significant volume of waste in countries with developed infrastructure. Recycled concrete aggregate (RCA) is currently an underutilized sustainable construction material due to a lack of available qualification and design standards concerning its use in construction activities. Due to the high volume of concrete waste produced during demolition activities, developing design and qualification standards for RCA is essential in reducing concrete waste in landfills and reducing the impact of concrete production on aggregate quarries. While many of the strength and durability characteristics of various RCA design mixtures have been studied, there are few standards for qualifying and processing RCA for use in new building materials. Previous studies have shown that good quality concrete can be produced using RCA, however there is wide variability in performance among similar mixtures. One area still not well understood that may contribute to variability is the role of the RCA’s parent concrete strength in the end properties of new RAC. The goal of this study is to assess the early and long-term mechanical property characteristics of various concrete mixtures containing lab-made RCA of a known parent strength at different coarse aggregate replacement levels. The compressive strength data obtained from these RCA design mixtures will be compared against RCA design mixtures made with the same virgin aggregate, but with field obtained RCA of an unknown parent strength. The results of this study will yield a better understanding of the effect of RCA parent strength and replacement level on the strength of a concrete mixture containing RCA.
Evaluating the Mechanical and Durability Performance of Recycled Plastic-Rubber Modified and Tire Steel Fiber-Reinforced Plastic-Rubber Modified Mortar Samples
Presented By: Qingli Dai
Affiliation: Michigan Technological University
Description: The mechanical and durability performance of both recycled plastic-rubber modified and tire steel fiber-reinforced plastic-rubber modified mortar samples will be evaluated with sample mixture design and lab tests. Recycled plastic-rubber aggregates, with mesh sizes from #10 to #18 partially replaced the fine aggregates with three volume percentages 10%, 15%, and 20%. Control mortar, mortar with recycled plastic-rubber and mortar with tire steel fiber reinforcement and recycled plastic-rubber 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 recycled plastic-rubber aggregates and tire steel fibers. The drying shrinkage and permeability tests were conducted to evaluate the durability performance of these sample types. These results will demonstrate the utilization of tire steel fiber and recycled plastic-rubber to improve the mechanical and durability performance of cement mortar.
Early-Age Expansion of Wastepaper Sludge Ash—Reduction and Benefits
Presented By: Ahmed Omran
Affiliation: New Jersey Institute of Technology
Description: Wastepaper sludge ash (WSA) produced from combustion of wastepaper sludge, wood residue, and barks in combusted fluidized bed plant has recently shown potential applications as a partial cement replacement in concrete. However, it exhibits expansion at early age. So, it is essential to either reduce the expansion of the WSA by special treatment or employ it where the expansion is favorable such as compensating the autogenous shrinkage and consequently the early-age cracking of concrete.
The current results showed the pre-wetting of WSA prior incorporating in concrete as a technique to reduce this expansion. The results conducted on mortar and concrete mixtures containing 20% pre-wetted WSA as cement replacement showed that the pre-wetting helps generating the expected disruptive hydration products before concrete setting, hence reducing the associated expansion problems and improved the strength.
The WSA was specially treated to form pellets with particle sizes 1-20 mm. The pellets are characterized by large porosity (17-43%) and was used as lightweight aggregates (LWA) in concrete. that can absorb high water quantity to reach saturated surface dry condition and release it during the concrete hydration to compensate the water in the capillary pores. Small- (1-5 mm) and coarse-size pellets (5-20 mm) was used to replace partially the sand and the coarse aggregates in concrete at rates up to 40%, as well as various combinations. Incorporating these pellets showed higher early-age expansion and consequently reduction in the net deformation resulted from the autogenous shrinkage. The results also showed workability enhancement with reduced superplasticizer demand.
HPFRC Made with Recycled Steel Fibers from End-of-Life Tires
Presented By: Alessandro Fantilli
Affiliation: Polytechnic University of Turin
Description: A detailed investigation on the use of large quantities of recycled steel fibers (RSF), obtained from end-of-life tires and used as an alternative reinforcement in structural concrete, is the object of this research. In particular, a large quantity of RFS is covered by a cement-based grout in new high-performance fiber-reinforced composites (HPFRC), cast with a two-stage procedure similar to that used for producing ferrocement. Mechanical properties are experimentally measured with bending and the uniaxial compression tests, performed on hardened concrete samples. In addition, the environmental impacts of HPFRC made with RSF, and with industrial steel fibers as well, are measured and then compared. The eco-mechanical analysis reveals the capability of the new HPFRC to effectively substitute similar cement-based composites manufactured with virgin materials. Accordingly, precast manufacts, such as corrugated slabs and manhole covers, can be produced without reducing the mechanical performances, but improving the environmental impact with a large volume of RSF.
Long-Term Performance Evaluation of Concrete Pavements Containing Recycled Concrete Aggregate in Oklahoma
Presented By: Xijun Shi
Affiliation: Texas State University
Description: To overcome the challenges associated with natural aggregate shortage and the disposal of construction and demolition waste, recycled concrete aggregate (RCA) has been increasingly used in Portland cement concrete (PCC) pavement as a virgin aggregate replacement. The work in this study involved conducting a performance evaluation of the existing RCA-PCC pavements in Oklahoma from different aspects, including laboratory determination of mechanical properties; a petrographic examination of the concrete; a field evaluation using a falling weight deflectometer (FWD) testing; and distress surveys to assess pavement behavior. The laboratory testing of the field cores confirmed that the addition of RCA into PCC causes a reduction in the modulus of elasticity and tensile strength; the reclaimed mortar was found to be the primary weak zone through which cracks pass. The surface condition survey data and analysis of the FWD results match each other, indicating that the RCA joined plain concrete pavement (JPCP) section exhibited lower performance compared with the control JPCP section. But this trend was not as definitive for continuously reinforced concrete pavement (CRCP). The relatively good performance of the RCA CRCP results from the section being rested on a stronger asphalt concrete base layer. Additionally, the inherent stiffness fundamental to the behavior of CRCP provides a superior level of protection of the base from erosion damage compared with a jointed pavement. The findings indicate that erosion-resistant base support and good load transfer are essential design considerations for JPCP made of RCA-PCC. CRCP appears to be more suitable for the use of RCA-PCC.