Climate change may corrode concrete even faster

[ I’ve paraphrased and shortened this article about how climate change will corrode concrete faster in the future from increasing carbon dioxide levels, and in coastal cities, from the chloride ions in sea spray. After that is the introduction section of the scientific article this Boston Globe story is based on.

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Hartnett, K. October 12, 2014. For concrete, climate change may mean a shorter lifespan. Two Northeastern engineers warn that a key building material is less solid than we think. Boston Globe.

Most Bostonian’s imagine rising sea levels as the worst threat from climate change.

But Northeastern University researchers civil engineer Matthew Eckelman and graduate student Mithun Saha say the largest vulnerability may be collapsing concrete, because rising temperatures from climate change accelerate the rate of decay.

This happens because reinforced concrete is susceptible to corrosion and decay as water gets through cracks and corrodes the metal rebar inside.  This is why our infrastructure is vulnerable even though there are concrete structures from the Roman Empire still standing – they didn’t use rebar to reinforce the concrete to prevent it from breaking easily of stretched or pulled.

By 2025 the first concrete coverings on buildings may start to fail, sooner than that if they weren’t built to code. By 2050 60% of Boston’s concrete buildings will be structurally deteriorating. Roads, buildings, bridges, and parking garages will eventually collapse.

Of Boston’s 1,700 concrete buildings about 57% were built in the 1960s, when it was still thought of as indestructible, until the 1980s and 90s when corrosion began. These early buildings also used weaker concrete than we have today.

The ocean’s chloride-rich salt spray makes matters worse as chloride ions penetrate the concrete, and carbon dioxide is also a problem as well, which will increase as temperatures rise. This means that structural trouble may arrive 25 years sooner than if temperatures remained the same as in the past, with structural problems in buildings in just 50 to 60 years.

The issue won’t be concrete landing on people below, but expensive repairs and higher costs for new buildings.

Fixes are expensive, such as thicker concrete, spraying rebar with green epoxy, or replacing steel rebar with aluminum bronze or carbon fiber.

Saha, M., Eckelman, M. September 2014. Urban scale mapping of concrete degradation from projected climate change. Urban Climate 9.

Introduction

Understanding the implications of climatic variation has become a critical issue for infrastructure maintenance planning. The Earth’s average temperature has been increased by 0.6 °C since the 1900s and is expected to increase by approximately 1.4–5.8 °C by the end of this century (McMichael et al., 2006). Many of the effects of climate change, including changes in temperature, pollutant concentrations, relative humidity, precipitation, and wind patterns, as well as increased frequency of severe events could have significant impacts on the operations and lifespan of critical and non-critical infra- structure (Rosenzweig et al., 2011). Infrastructure capacity could be acutely overwhelmed (e.g., sea walls failing due to storm surge) or degraded gradually. Assessing the potential impacts of climate change on the built environment is difficult, as the relationship between material degradation and cli- mate is complex (Cole and Paterson, 2010). The Northeastern United States is likely to see an increase in extreme precipitation events as well as overall increases in temperature and relative humidity (Stocker et al., 2013)

Climate-induced damages to urban infrastructures are of particular concern. Urban areas in the United States currently include approximately 250 million residents, projected to grow to 365 million by 2050 (U.S Census Bureau, 2010). While the urban share of population and economic output in the US has grown in the past decades, much of the existing urban infrastructure has become increasingly susceptible to failures (Solecki and Marcotullio, 2013; Wilbanks, 2012). Aging buildings and transportation, energy, water, and sanitation infrastructure are all expected to become more stressed in their ability to support existing services for urban residents in the coming decades, especially when the impacts of climate change are added as stressors (McCrea et al., 2011). Climate change will also contribute directly to physical degradation of infrastructure and building materials (Nijland et al., 2009).

While much research on climate change impacts has focused on infrastructure susceptibility to extreme events and flooding from long-term sea level rise (Anderson and Boesch, 2009), relatively few studies have been carried out on the direct effects of climate change on the structural deterioration of infrastructure. One direct mechanism is acidic attack of cementitious materials. Concrete degradation due to acid rain has been extensively studied (Zivica and Bajza, 2001), and elevated levels of atmospheric CO 2 will increase the formation of carbonic acid in precipitation. Similarly, uptake of CO 2 by the oceans and the resulting decrease in pH will amplify degradation of structures in urban coastal areas that are exposed to seawater (Greaver et al., 2012).

Another mechanism for climate-induced concrete degradation is through early failure of the protective concrete cover over reinforcing steel, leading to corrosion and spalling, due to changes in CO 2 and temperature (Talukdar et al., 2012a; Mehta and Monteriro, 2006), which has only recently been analyzed. Yoon et al. (2007) was among the first to consider the effects of climate change on concrete performance and lifetime, in particular the effect on carbonation rates; however, this model does not account for the influence of temperature change, which can significantly affect the diffusion coefficient of CO 2 into concrete, the rate of reaction between CO 2 and Ca(OH) 2 , and the rate of dissolution of CO 2 and Ca(OH) 2 in pore water. The model is also a time-independent predictive model that assumes CO 2 concentrations to be constant up to a given time, thereby underestimating carbonation depths under changing atmospheric conditions (Stewart and Peng, 2010). Stewart et al. (2011) built on the work by Yoon et al. (2007) by taking into account the effect of temperature on the diffusion coefficient, but they did not consider the influence of temperature on the other aforementioned parameters. Their work looked not only at carbonation and chlorination, but also at the time to crack initiation, crack propagation, and failure due to reinforcement corrosion. Similar carbonation and chlorination models were used by Stewart et al. (2011) in their work, who noted that there is a need for an improved model that considers the time-dependent effect of CO 2 concentration and other parameters such as temperature and relative humidity.

Recently, Talukdar et al. (2012a) estimated carbonation (but not chlorination) penetration depths in concrete due to projected climate change. Several deterministic model parameters were experimentally verified using unloaded/undamaged concrete. They reported 25–35 mm increase in penetration depth due to carbonation alone. Separately, Bastidas-Arteaga et al. (2010) investigated the influence of global warming on chloride ingress into concrete using a stochastic model of chloride penetration and corrosion initiation. Their particular approach was to model future weather conditions, recognizing that temperatures will ?uctuate not only over the century, but also during a given year, and that the duration of the hot season throughout most of the world is expected to lengthen over this century. They found significant correlation between chloride ingress over time associated with projected global warming. Talukdar et al. (2012b) then improved their carbonation model and coupled it to the climate model proposed by Bastidas-Arteaga et al. (2010) to project concrete infrastructure degradation and to consider the suitability of current code requirements.

The current study builds on these previous reports by estimating climate-induced changes in cor- rosion depths for both carbonation and chloride induced corrosion for multiple climate scenarios and at a high level of geospatial resolution.

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