Durability is one of the most important requirements for sustainable infrastructure. Federal, state, and local agencies expend significant effort to maintain the quality and condition of aging civil structures, especially those in aggressive service environments. Among many factors, durability influences the service life and integrity of concrete materials and structures. Extensive research has been conducted to understand the deterioration mechanisms of concrete in an effort to extend the longevity of concrete members. In this session, presentations of both experimental and analytical investigations are of interest, which may include the durability of concrete structures reinforced with steel or fiber-reinforced polymer bars, modeling of service life for concrete under aggressive environments, and the structural integrity and resilience of rehabilitated members. The session emphasizes recent research findings and provides an opportunity to discuss present challenges and technical issues. Critical information is given to those who lead tomorrow’s structural design and construction with an emphasis on durability, service life, and integrity, including practicing engineers, government officials, and academics.
(1) Define the state of the art of structural performance subjected to environmental and mechanical distress;
(2) Identify research needs to advance the knowledge associated with the durability, service life, and integrity of concrete bridges and buildings;
(3) List efforts to establish a new trend in the design and construction of concrete bridges and structures;
(4) Link laboratory investigations with practical site application.
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.
Durability of Internally Cured Concrete with Supplementary Cementitious Materials
Presented By: James Lafikes
Affiliation: Genesis Structures
Description: Internal curing (IC) via pre-wetted lightweight aggregates in conjunction with supplementary cementitious materials (SCMs) in high-performance concrete (HPC) has emerged as an effective measure to reduce cracking in bridge decks. The high absorption of lightweight aggregates, however, means durability remains a concern with these technologies. Scaling and freeze-thaw tests have been completed for concrete mixtures containing IC and SCMs (partial replacement of portland cement with slag cement) to identify the key factors affecting durability in bridge decks. Results indicate that scaling resistance is governed by maintaining an adequate air content; mixtures containing less than 7% exhibited more damage than similar concretes with higher air contents. Freeze-thaw durability is governed by the total amount of internal moisture of concrete (IC plus water absorbed by the normal weight aggregates). Crack surveys of bridge decks containing IC and SCMs show a low amount of cracking in the years following placement, but durability issues (damaged grooves and aggregate pop outs) are noted for mixtures containing an air content below 7%, high amounts of internal moisture (above 12% by total weight of cementitious materials), and late-season placement dates that did not allow the concrete to dry out prior to being exposed to deicing salts and freezing conditions.
Durability of Fiber-Reinforced Concrete Fireproofing in Aggressive Industrial Environments
Presented By: Nicholas Triandafilou
Affiliation: Brindley Engineering Corporation
Description: Fireproofing deterioration is widespread in industrial facilities throughout the country. Spalling concrete has potential to damage equipment and harm personnel. Replacing concrete fireproofing like-in-kind does not eliminated the hazard as spalls could potentially occur again over time. However, when properly designed and installed, concrete is a durable option for replacing deficient fireproofing in aggressive environments. This paper presents the results of a case study on a structure in a Midwest industrial complex. Extensive concrete fireproofing repairs were performed on the structure 12 years ago. Design requirements included normal weight concrete with polypropylene fibers which enhance durability by improving cracking resistance. During a fire, fibers melt, forming relief channels for moisture to escape, thus eliminating explosive spalling. Installation methods included WWR with positive anchorage to structural steel. WWR was attached to post-installed adhesive anchors between column flanges where existing fireproofing was sound and difficult to remove. After 12 years in service, repairs exhibit no significant defects. This level of durability is attributed to the design and installation methods utilized. Concrete fireproofing is a durable option for fire protection, provided structures are designed to support its weight, its mix design is properly proportioned, and it is adequately anchored and reinforced.
Durability of Highly Flowable Self Healing Concrete under Freeze Thaw Actions
Presented By: Jialuo He
Affiliation: Washington State University
Description: This laboratory study used the UF (Urea-formaldehyde) microcapsules and PVA (polyvinyl alcohol) microfibers as a self-healing system to improve the durability of concrete in cold climates. The resistance of this self-healing concrete to freeze-thaw cycles were evaluated by measuring the change of relative dynamic modulus of elasticity (RDM) with respect to the number of freeze-thaw cycles. The control specimens (either with or without PVA microfibers) approached the state of failure and the corresponding RDM dropped 38% after being subjected to 54 freeze-thaw cycles. However, the UF microcapsules alone could increase the number of freeze-thaw cycles that concrete can withstand from 54 to about 600 and the associated RDM drop was reduced to 10%. With the aid of PVA microfibers, this self-healing system exhibited an even better performance that the associated RDM drop was almost 0% by the end of 600 freeze-thaw cycles. The 3-D X-Ray micro-computed tomography (CT) was employed to investigate the microstructure of the concrete specimens after being subjected to 300 freeze-thaw cycles. Based on the reconstructed 3-D images of internal void system, the empty microcapsules after the healing agent being consumed played an important role in providing extra space for the volume expansion of the internal liquid due to freezing. The voids size distribution and fraction of each type of voids revealed that part of the microcracks with a size smaller than 100 µm were healed. The authors established a nonlinear polynomial relationship between the RDM and the number of freeze-thaw cycles (N). In addition, we employed the Weibull distribution model to conduct the probabilistic damage analysis and characterize the relationship between N and damage level (D) with different reliabilities.
Corrosion Related Durability of Steel Reinforcement in a Novel Concrete Material
Presented By: Christopher Alexander
Affiliation: University of South Florida
Description: A non-hydraulic, low-lime calcium-silicate cement (CSC) can be produced with 30% reduction in CO2 emissions when compared to ordinary portland cement (OPC). Durability testing has shown its ability to withstand freeze-thaw resistance to alkali-silica reaction and sulfate attack, however, CSC-based concrete’s ability to protect reinforcing steel against corrosion has not been reported. Cured CSC-based concrete has a lower pore water pH (~ 8.5 to 11) than OPC-based concrete making corrosion initiation relatively easier. However, CSC-based concrete has a higher electrical resistivity than OPC-based concrete, making corrosion macrocells less efficient. This work presents experimental results comparing the corrosion durability of two formulations of CSC-based concrete to that of one type of OPC-based concrete. The array of corrosion experiments includes exposure to fresh water and salt water (15 days of each alternate wetting and drying regimes) and a high humidity environment. Corrosion performance was evaluated by half-cell potential, macrocell current and electrochemical impedance spectroscopy. Selected samples have been autopsied to acquire visual and micrographic evidence of the state of corrosion and assess the corrosion product composition and transport within the concrete. Additionally, accelerated corrosion propagation tests were performed to assess the ability of each concrete formulation to accommodate corrosion products as an indicator of the duration of the corrosion propagation stage.
Influences of Nonionic Surfactants on Structure, Reactivity and Efficiency of Montmorillonite in Mitigating Alkali-Silica Reaction
Presented By: Jianqiang Wei
Affiliation: University of Massachusetts Lowell
Description: To address the challenges of using clay minerals in concrete, two nonionic surfactants, Triton-X-100 (TX-100) and polyethylene glycol-10 (PEG-10), have been employed to modify a commonly used clay: sodium-montmorillonite (sMT). The crystallinity, interlayer spacing, amount of intercalated surfactants, dispersion, moisture and water absorption, and swelling behavior of the clays were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), attenuated total reflection-Fourier transforms infrared (ATR-FTIR) spectroscopy, UV-vis spectroscopy, dynamic vapor sorption (DVS), and swell index test. The pozzolanic reactivity of the nonionic-surfactant-modified sMT was evaluated through lime consumption and isothermal calorimetry tests. The roles of the raw and modified sMT in mitigating alkali-silica reaction (ASR) were also investigated by partially replacing cement in concrete containing reactive aggregates. The results indicate that both TX-100 and PEG-10 can be intercalated into the interlayer space of sMT, which resulted in improved dispersion of sMT in concrete pore solutions, increased swelling indexes and d-spacing, and thus raised water absorption capacity and pozzolanic reactivity. More significant mitigation of ASR-induced concrete expansion was observed from the modified clay samples indicating that nonionic surfactant treatment is an effective approach to enhance the role of clay minerals in durable concrete design.
pH-Dependent Chloride Desorption Isotherms of Portland Cement Paste
Presented By: Mahmoud Shakouri Hassanabadi
Affiliation: Colorado State University
Description: Carbonation, sulfate, and acid attack can lead to the release of bound chlorides, which in turn can increase the concentration of free chlorides in the pore solution. Although the release of bound chlorides (i.e., chloride disassociation) can significantly increase the risk of corrosion and reduce the service life of reinforced concrete structures, there is scant information on the disassociation kinetics of chlorides as a function of the pH of the pore solution in cementitious systems. The objective of this study is to develop pH-dependent chloride desorption isotherms for ground ordinary portland cement (OPC) paste exposed to MgCl2, CaCl2, and NaCl solutions. The results of this study show that the Langmuir isotherm suits the chloride binding of ground OPC paste better, and the amount of bound chloride is predominantly influenced by the cation type of chloride in decreasing order of CaCl2 > MgCl2 > NaCl. The addition of nitric acid to the ground cement paste can initially result in the total disassociation of the bound chlorides from MgCl2 and NaCl salts. However, only 58% of bound chlorides from the CaCl2 solution can be dissociated as a result of the reduced pH of the exposure solution. Further addition of nitric acid results in the formation of a calcium-rich hydrogel that is capable of absorbing free chlorides.
Development of a Standard Practice for Service Life Prediction
Presented By: Kyle Stanish
Affiliation: Tourney Consulting Group, LLC
Description: In response to sustainability concerns and a desire for long-lasting infrastructure, durability design and service life prediction have been more frequently incorporated into design requirements from Owners. It is not enough to say that your new structure will last long enough based on customary construction practices, but the Designer or Contractor is being asked to prove it. While Owner know that they want and need service life prediction as part of the design deliverable, this is still a new service and standards for performing a service prediction are still be developed. ACI Committee 365 is developing a standard practice to simplify the requesting of service life prediction services for the Owner and to provide a uniform basis for performing and documenting a service life prediction by practitioners. The objective is to improve the quality of the predictions that are being made.