Influence of climate change on concrete durability in Yucatan peninsula

Influence of climate change on concretedurability in Yucatan peninsula

P. Castro-Borges* and J. M. Mendoza-Rangel

The environmental effects of global climate change (GCC) are becoming more evident.

Nonetheless, efforts to document its effects on the durability of infrastructure are still limited.

The present study used long term data (19612008) on temperature, relative humidity,

precipitation and evaporation recorded in a tropical microclimate of the port of Progreso

(Yucatan, Mexico) in order to detect climatic patterns associated to GCC. In addition, the authors

analysed chloride profiles in concretes of different quality but of the same age (15 years) and

exposed to the same microclimate. Results suggest the presence of environmental changes

associated to GCC during the last 40 years, especially in terms of average and maximum

temperature, which showed increases of 1 and 0?22uC per decade respectively. Results alsoshowed that seasonal and multiannual climatic cycles had an influence on the behaviour of the

chloride profile of the studied concretes and thus on their durability.

Keywords: Global climatic change, Temperature, Infrastructure, Chlorides, Concrete, Durability

IntroductionGlobal climate change (GCC) is a reality and has beenproperly documented during recent years.1 Carbon dio-xide and other contaminants accumulate in the atmo-sphere and trap the heat, thus causing an overallincrease in global temperatures. This gradual increasein temperature has become evident and has causedchanges, such as negative effects on human health2,3 viaheat waves and diseases, changes in ecosystem function,which have lead to species loss,4 increase in ocean tem-peratures,5 which have led to glacier melting, changes inthe timing of melting and an increase in ocean level,68

and changes in climate patterns characterised by anoverall increase in temperature,9 more frequent andsevere droughts, fires and storms. Nonetheless, very littleinformation exists with respect to GCC effects on steeland concrete infrastructure,1012 potentially resulting ina decrease in infrastructure durability. For example,more frequent and intense hurricanes carry rains withchlorides from the sea, which impact the infrastructureof sites that were originally not designed or constructedwith such greater frequency or intensity of effects inmind. As a result, infrastructure deterioration may occurat an accelerated rate, and infrastructure service lifedecreases substantially.

Preventing or minimising infrastructure effects due tohurricanes may be feasible and realistic. However, mid-and long term effects of GCC on concrete infrastructureare still unknown, and it is not clear how they can betested for. One relevant aspect which deserves attention

is the infrastructure chemical changes, such as thetransportation of aggressive agents (e.g. chlorides) as aresult of changes in temperature. Chlorides, for instance,are the main cause of metal corrosion in concrete struc-tures. Nonetheless, previous studies have only focusedon the risks of GCC effects on concrete structures atlarge scales10 as a result of major climatic events, such ashurricanes, flooding, strong rains, etc., as well as ways toprevent or minimise these climatic effects.

The present study is based on a recompilation of43 years of microclimatic data from a site located at theport of Progreso (Yucatan, Mexico). These data were usedto test for an influence of recent GCC on concrete chlorideconcentration, which is the main cause of deterioration ofconcrete structures exposed to coastal environments. Themain objective of this work was thus to detect evidence ofGCC during the last four decades and relate GCC as wellas multiyear and seasonal climatic variation to thebehaviour of the chloride profile of concretes of differentquality exposed to a coastal environment.

ExperimentalConcrete specimens of different quality and curing timect were exposed to a coastal environment since 1993 andwere located at different distances from the coastline inProgreso, Yucatan (21u169330 N and 89u399140 W). Forthis study, the authors used data recorded from speci-mens located at a station, which was 100 m inland fromthe coast and with compression strength f9c of 150, 250and 350 kg cm22, water/cement ratios w/c of 0?46, 0?53and 0?76 and a ct of seven days.

Climatic dataThe authors obtained climatic data from the CentroMeteorologico de la Comision Nacional del Agua to

Centro de Investigacion y de Estudios Avanzados del IPN, Unidad Merida,A.P. 73 Cordemex, CP 97310, Merida, Yucatan, Mexico

*Corresponding author, email [email protected]

2010 Institute of Materials, Minerals and MiningPublished by Maney on behalf of the InstituteReceived 16 April 2009; accepted 29 July 2009DOI 10.1179/147842209X12489567719662 Corrosion Engineering, Science and Technology 2010 VOL 45 NO 1 61

characterise the microclimate of the sampled station.Data consisted of maximum temperature, average tem-perature, rainfall, relative humidity and evaporation,from 1961 (in some cases 1970) to 2008. The authorsused annual means of each variable for statisticalanalyses.

MaterialsCylindrical concrete specimens of 7?5615 cm werefabricated. Thirty of these probes were made only ofconcrete to monitor chlorides and carbonation, whileanother 30 were made with a steel bar and a referenceelectrode (RE) embedded in the concrete in order tomonitor corrosion patterns. A total of 60 probes werepresent at this sampling station. Both types of probeswere simultaneously exposed to environmental condi-tions since 1993, which means that both groups weresubjected to aggressive effects such as salt in the air,carbonation, high temperatures, rainfall and high rela-tive humidity.

Aggregates

Probes were fabricated using crushed aggregatesbrought from a quarry, which was close to the coastand which supplies material to most of the constructioncompanies that operate in the north of Yucatan. Thegranulometric analysis showed that the coarse grained

portion showed an acceptable gradation, while the sandportion had an excess of fine material. The selection andcharacteristics of these materials were determined basedon typical conditions observed in the region.

Cement

The authors used an ordinary Portland cement (OPC),which was fabricated locally. Physical and chemicalproperties of the cement are shown in Tables 1 and 2.

Water

Tap water was used for mixing, and during the curingstage, 2% of limestone was added to the water in orderto increase the pH and, in this way, avoid the loss ofalkalinity during the fabrication process.

In order to have an idea of the corrosion potential ofthe materials before their use, the authors recorded theirchloride content before they were exposed (results arepresented in Table 3). These measurements showed thatthe materials used were below what is consideredaggressive based on standards ACI-201 and ACI-318.13

Reinforcement steel

The authors used A no. 3, grade 42, reinforcement steel,which was fabricated locally following specificationsfound in the Mexican standards NOM-B-6-1993 andDGN-B-434-1969 (according to the manufacturersrecords).

Concrete

Three types of concrete were used based on the w/cfabrication ratios used (w/c50?76, 0?53 and 0?46), ofwhich the most commonly used is 0?76 in the case ofconstructions, which are periodically supervised such ashouses. A w/c ratio of 0?53 is common for buildings suchas schools, while 0?46 is rarely used based on theenvironmental conditions present in the region. Thecompressive strength f9c as a function of the w/c ratio isgiven in Table 4. Despite strong variation in tempera-ture typically observed in the study region, concrete isusually cured for one to three days in the case ofmaterial used for houses and constructions that are notsupervised. Specified curing time for schools and govern-ment buildings is of 728 days, although in practice, itusually does not exceed seven days. Based on this, thepresent study used a curing time of seven days as well asw/c ratios of 0?46, 0?53 and 0?76.

Experimental cellSpecimen design

A cylindrical mould was used to fabricate the specimens.A hole was made at the base of the mould to provide

Table 1 Chemical properties of OPC used in presentstudy

SiO2 21.30Al2O3 4.67Fe2O3 4.19CaO 64.98K2O 0.16 3.50% (max.)SO3 2.62Ca 1.48MgO 0.83 5.00% (max.)C3S 52.00C2S 22.00C3A 5.00C4AF 13.00Ign 1.50 3.00% (max.)Ins 0.47 0.75% (max.)

Table 2 Physical properties of OPC used in presentstudy

Specific surface Blaine method 3532 2800 cm2 g21

Fineness US 200 97.85US 325 88.63

Vicat Initial 133 0.45 hFinal 165 8.00 h

False setting Per cent penetration 69 50%Autoclave Per cent expansion 0 0.80%Compressivestrength

24 h 83Three days 203 130 kg cm22

Seven days 255 200 kg cm22

Table 3 Estimation of total chloride ion content for material used to fabricate concrete cylinders*

Ingredient Chloride contents in ingredients Typical chloride contents (ACI-318 building code)

Cement 8,78 ppm 50100 ppmSand 0,0227 pwa 0.0010.04 pwaCoarse aggregate 0,0207 pwa 0.0010.04 pwaWater 213 ppm No more than 250 ppm

*ppm, parts per million, pwa, per cent per weight of aggregate.

Table 4 Compressive strength of 15630 cm concretecylinders used according to ASTM C39

w/c ratio 0.76 0.70 0.53 0.50 0.46f9c, kg cm22 157.00 172.50 221.50 290.33 269.67

Castro-Borges and Mendoza-Rangel Influence of climate change on concrete durability in Yucatan

62 Corrosion Engineering, Science and Technology 2010 VOL 45 NO 1

two exits for the steel in order to avoid segregation orspills during the steelconcrete interphase. One Ti/IrO2bar was embedded in the concrete and used as a RE forcorrosion measurements; the RE had been previouslycharacterised.14 The RE was located between the steel barand the concrete surface and exactly at the midpointbetween the two extremes of the cylinder. Previous tosetting the concrete, the reinforcement steel received atreatment which consisted of weighing the steel asreceived from the manufacturer, applying an epoxy coverand using a tape to limit the sampling area and isolatingits surface from the air at the concretesteel interphase.This was done to avoid cracks in the concrete, whichwould cause undesired penetration of chlorides or theformation of cells with differential aeration.15

The mould was sealed, and the concrete was set oncethe ER and the steel had been placed in the mould.Special care was taken to construct the specimens withequal w/c ratios and curing times and that the fabrica-tion process was conducted by only one person. Speci-mens were stored after the curing period, and beforethey were exposed to the environment, they were paintedwith an epoxy cover to control which areas were to beexposed to environmental conditions and protect theareas for which the effect of aggressive agents was notdesired (Fig. 1). After a series of initial tests (CO2, Cl

2,etc.) the probes were exposed to the environment. Theauthors had two specimens with embedded steel and twowithout steel for each combination of variables (w/c andct).

Chemical analysesChlorides and carbonation

The faces of the cylinders made only of concrete weresealed with wax to assure that CO2 and Cl

2 penetration

occurred only in a radial direction. A slice of each speci-men was cut before exposure and when the corrosionparameters started showing apparent values of0?2 A cm22 in the steel for any of the specimens, whichhad an embedded reinforcement. This value is consid-ered as the standard critical value for the apparentcorrosion current density Icorr, which indicates damageto structures that are influenced by Cl2 and CO2.

16 Onthe dry part of the recently obtained slice, a dissolutionof ethyl alcohol with 1% of phenolftalein was applied toassess carbonation depth.17 The powders which arenecessary for the extraction of Cl2 were obtained bymeans of a drill and were sifted with a no. 50 sieve.18

Previous studies have reported that free chlorides maydepassivate steel and that under these conditions waterextraction is recommended.19 Nonetheless, it is clearthat carbonation has an influence, and thus, it maycontain more free chlorides. Because a potential riskmay exist because of this situation, it should beevaluated, and this is why the authors conducted anacid extraction of total chlorides.17 Based on previoustests conducted by the authors, as well as from otherstudies,19,20 an extraction technique was developed,which produced results that coincided with thoseobtained from techniques specified in standards ASTMC144 and UNE-217. This method consists of drying apowder sample at 105uC for an hour. Once this dryingperiod has concluded, samples are placed in a desiccatorfor 15 min. A 2?5 g subsample is then obtained anddiluted in 100 mL of a 0?06M HNO3 solution, which issubsequently agitated for 10 min. The resulting solutionis appraised to 125 with the 0?06M HNO3 solution andis allowed to sediment for an hour, after which thesample is filtered with Whatman paper no. 2. Fiftymillilitre subsamples are then taken from the filteredsolution to which 1 mL of a 5M sodium nitrate solutionis added. These subsamples are then agitated at a con-stant velocity, and the concentrations are read followinginstructions from a selective ion electrode (Orion 9417-00, 9002-00).

Results

Climatic dataFigure 2 shows data for maximum temperature, averagetemperature, rainfall, relative humidity and evaporation.In all cases, a gradual increase was observed from 1961to 2008, which is confirmed by the tendency line whichalso predicts that this behaviour will continue duringthe following years. This linear tendency was morepronounced in the case of maximum temperature.Interestingly, multi-year cycles were observed for allvariables.

Figure 3 shows accumulated values and tendency linesfor each value for each of the recorded variables, andalthough it is recognised that this result is of no realphysical value, useful information may be obtained asfor example variation in climatic parameters remainedconstant and showed a systematic pattern throughoutthe period of study.

ChloridesFigure 4 shows chloride profiles recorded for the speci-mens at 0, 24, 45, 78 and 126 months after exposure. Thegreatest chloride concentrations recorded at 0 and 24months occurred for specimens with the lowest f9c, while

1 Schematic representation of one of concrete speci-

mens used in present study


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chloride content decreased for specimens with greaterresistances. This makes sense because the w/c ratioimproves when f9c is greater, making the structure lessporous and thus limiting chloride diffusion.

Nonetheless, after 45 months, chloride concentrationinside the probes was more variable. This suggests thatconcrete quality is not the only factor influencing themovement of these aggressive agents and that otherparameters may have an effect. As discussed ahead,atmospheric parameters are of great importance inexplaining the observed results.

Discussion

To the authors knowledge, there have been no studieswhich have looked at the combined effect of GCC andmicroclimate on infrastructure durability in the Yucatanpeninsula. Although there is available information onthe penetration mechanism21 and interpretation ofchloride profiles for concrete structures exposed totropical coastal environments of the region,22 long termdata had not been recorded yet, and it has not beenlinked to atmospheric records. Thus, findings from this

2 a maximum temperature, b mean temperature, c rainfall, d relative humidity and e evaporation

3 Accumulated values for a maximum temperature, b mean temperature, c rainfall, d relative humidity and e evaporation:

values showed constant variation through time



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study allow a discussion on climate change effects oncorrosion mechanisms in concrete structures.

Seasonal and multiyear climatic cyclesBased on Fig. 2, a cyclic pattern can be observed for allof the atmospheric parameters included in the study,each cycle lasting a more or less constant number ofyears. Although there are some differences in cycleamplitude and frequency, cycles continue despite theannual increase in temperature. Previous GCC studiesand reports included in this study1,2327 do not discussthis cyclic behaviour in detail. It is interesting to notethat the frequency of cycle periods is not annual butmultiannual and that each cycle lasts ,10 years (Fig. 5).This finding suggests that the observed pattern may notbe governed by local atmospheric conditions but byexternal factors such as the Earths movement aroundthe sun, which could in turn be affected by changes insolar activity such as periods of high sunspot activitywhich occur approximately every 11 years and describecycles.28,29 Based on this, the multiyear cyclic patternappears not to be affected by local phenomena such asthe increase in temperature due to the emission ofgreenhouse gases. Thus, regardless of greenhouse gasconcentrations increasing or decreasing after the Kyotoprotocole30 and thus of future increases in global

temperatures,31,32 the observed cyclic pattern is expectedto continue. Although these arguments may explain, atleast in part, the observed multiyear cyclic pattern forclimatic parameters, more evidence is needed tocorroborate this pattern. Nonetheless, the data pre-sented here suggest that despite current effects of globalwarming on the planet, multiyear climate cycles may notbe altered, at least not dramatically, but calls for futureresearch initiatives, which look into these patterns andtheir implications in the context of GCC.

Changes in amplitude and/or frequency in the multi-year cycle have also been reported in previousstudies,1,2327 and although these studies were conductedat greater spatial scales, they show evidence of the sameperiodic pattern in temperature. In fact, most reportsindicate that the highest temperatures were recorded forthe 1990s, mostly in 1998, which agrees with the datashown in Fig. 5. This same figure suggests that anotherpeak in temperatures will soon take place.

If the observed climatic behaviour were to be con-firmed in other microclimates, then perhaps this infor-mation would represent a useful tool to understand andcontrol the effects of multiyear cycles on agriculturallands or urban areas, which are affected by variation inclimatic conditions.

On the other hand, between season variation inclimatic parameters was also clearly observed (Fig. 6).

a 0 month; b 24 months; c 45 months; d 78 months; e 126 months4 Chloride concentration profile at different penetration depths, compression strengths and times during study

5 Multiannual cycles of maximum temperature observed

at study site 6 Seasonal temperature versus time



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Maximum temperature values from 1970 to 2008exhibited a cyclic behaviour, which was similar for allfour seasons, including a gradual temporal increase inmaximum temperature for each season; maximumtemperatures were greatest during spring (April toJune). This suggests that external factors not onlyfavour a multiyear cycle for maximum temperaturesbut may also be responsible for a seasonal cyclic patternfor this variable. For instance, if more data supportedthe idea that sunspots are responsible for the observedmultiannual temperature behaviour, then peaks intemperature as well as their duration may be used topredict seasonal and annual maximum temperaturevalues. Figure 5 shows that temperature multiyear cycleshave a duration of ,10 years, which suggests that, in2012, another peak in temperature will take place, whichshould coincide with a predicted period of high sunspotactivity.28

Based on this, the authors conclude that a multiyearpattern of maximum temperature values is described bythe data, and this pattern may be controlled by extrinsicfactors, that is, phenomena which take place outsidelocal atmospheric conditions such as sunspot activity,which describes cycles that coincide with the observedclimatic pattern. Likewise, annual cycles (betweenseason) in maximum temperatures were also observedand were of a particular intensity depending on theseason. These intra-annual cycles are controlled mainlyby local atmospheric conditions.

Gradual increase in annual maximumtemperatureMicroclimatic data recorded at the study site indicatedthat, despite multiyear cycles, temperature valuesexhibited a steady increase. From 1970 to 2008, annualmaximum temperature values increased by 4?2uC, whilemean temperature values from 1961 to 2008 increased1?1uC. This means that maximum and average tempera-ture values showed a per decade increase of 1 and 0?22uCrespectively (as shown in Fig. 2a and b). Such values arelarger than those reported previously in the literature,9,10

including the intergovernmental panel on climate change(IPCC) report,1 which reports an increase in 0?13uC perdecade. None of the studies included in this work2327,33

reported temperature increases as large as the averagevalue found here, although it should be noted that themicroclimate used here is considered dry very warm andwarm.34

Maximum temperatures are probably the singlevariable which have the greatest negative effect onecosystems and has a large influence on GCC effects.Nonetheless, no studies have so far looked at long termpatterns and predictions for this variable at the studyregion. Although previous studies make use of sophis-ticated computer models to predict future temperaturepatterns,35 it is also important to generate empiricalmethods which make model predictions more robustand easy to use and, in this way, analyse the potentialrisks that such temperature changes will bring and maketimely decisions. Figure 7 shows a graph with themaximum temperatures of each multiyear cycle andalso provides a linear tendency with an almost perfectfit. Nonetheless, it is evident that there are a series ofadditional factors which could influence the observedtendency, and although the linear fit is not surprising,

predictions remain uncertain. The tendency line indi-cates that by 2010, average temperature will increase by0?3uC compared to 2008 and that, by years 2020 and2030, temperature will increase by 1 and 2uC respectivelycompared to 2010. In other words, the rate of tem-perature increase would be consistent with what hasbeen observed at the study site during the last 30 years.Although this 1uC increase per decade may not beconstant in the future, at present, it represents usefulinformation, which should be considered in decisionmaking processes.

Based on this, the authors conclude that the observedincrease in maximum temperature during the last fourdecades, based on maximum values of each multiyearcycle, is evident and appears to follow, at least at themoment, a well defined linear tendency. This finding isrelevant for future climate change predictions andprovides relevant information for studies and strategiesdesigned to understand and limit the impact of GCC onhuman infrastructure and natural ecosystems.

Multiyear cycles and seasonal climatic effectson concrete infrastructureGlobal climate change studies included in this work havefocused mainly on the effects of climate change onnatural resources, such as water,5 increase in sea level,68

global warming,9 negative effects on agriculture,4 melt-ing of polar caps36,37 and risk of infectious diseases.2,3

However, very few have looked at GCC effects onconcrete infrastructure,1012 and the focus of suchstudies has not been the durability of concrete butinstead potential risks associated to torrential rains,flooding and hurricanes as well as measures whichshould be taken when building new structures consider-ing climate change effects.

Undoubtedly, the microclimate studied in this workshowed clear evidence of GCC during the last 40 years,specifically an increase in temperature (Fig. 2a). Suchincrease in temperature remained despite a multiyearcycle pattern, and this can be observed based on thelinear tendency shown in Fig. 2a. On the other hand,Fig. 8 shows chloride concentration profiles which aretypical of probes exposed to the studied microclimate.Under these conditions, the authors expected drasticchanges in the chloride profile due to the aggressivenessof events, such as rains, winds, drought, etc. Indeed, asshown in Fig. 8, independently of concrete quality, acharacteristic chloride profile can be observed for eachseason. Short term studies, including those which havebeen conducted in the studied microclimate,22 havereported an accumulation of chlorides over time,especially at sampling sites located close to the steel

7 Maximum temperature values for each multiyear cycle

and temperature prediction with linear trend



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bar. These results suggest that a saturation point may bereached after a given amount of time. Nonetheless, longterm studies such as the present work not only show anincrease in chloride amount over time but also multiyearcycles, which had not been previously reported in theliterature (Fig. 9). Such cyclic pattern is most likelyrelated to the multiyear atmospheric cycles previouslydiscussed. Previous studies agree that concrete infra-structure is influenced by environmental conditions;however, all of the information generated so far comesfrom short term studies, and the influence of additionalfactors driving or at least affecting a multiyear cycle hasnot been discussed yet. The fact that concrete chlorideamounts vary in a multiyear manner may offer a newway of analysing and determining concrete structuredurability and service life and is relevant in terms ofpredictions and damage control in concrete due toatmospheric effects. These findings offer a new para-digm, which refers to multiyear view of climate effectson the durability behaviour of concrete structures, atleast with respect to chlorides and corrosion. However,it will be necessary also to describe the corrosionbehaviour of concrete structures under periods ofextreme heat and drought, as corrosion velocity maydecrease considerably under these conditions.

Total chloride cycles recorded for each specimen areshown in Fig. 9. This figure not only shows internalglobal variation through time but also how thisvariation matches that of multiyear cycles in atmo-spheric variables (Fig. 10, which indicates when thechloride profiles were recorded). The lowest inflectionpoints corresponded to time periods for which both

chloride concentrations and maximum temperaturevalues were lowest throughout the cycle.

Temperature, as well as other parameters, showed amultiyear cycle pattern. For time recorded in thechloride concentration profiles, a complete cycle oftemperature is obtained. However, it has no coincidencewith the atmospheric multiyear one, but curiously, itcould be replicated in other cycles (Fig. 10). During themultiyear climate cycle, which included the reportedchloride profiles (Fig. 10), the latter showed an increasein quantity, and when the following multiyear cyclestarted, the chloride profile also started a new cycle. Thisresult was clear and was observed for all of the recordeddata in this study. If the authors had not included theatmospheric data, the observed temporal pattern ofchloride concentrations would have probably beeninterpreted as human introduced error during data

a a/c50?76, f9c5150 kg cm22; b a/c50?53, f9c5250 kg cm22; c a/c50?46, f9c5350 kg cm22

8 Chloride profiles versus time

9 Total amount of chlorides recorded for concrete

specimens

10 Multiyear cycles and chloride sampling periods after a

0 month, b 24 months, c 45 months, d 78 months and

e 126 months



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collection. However, measurements were repeated withthe remaining material, and the results were consistent.

Evidence of GCC was observed in this study based onthe multiyear cycles for the measured variables as well asthe gradual increase in temperature throughout thestudy period. This scenario has an effect on chlorideconcentration profiles which damage concrete infra-structure, especially in coastal marine environments.Nonetheless, knowledge on the existence and durationof climatic multiyear cycles offer a relevant tool toprevent damage on concrete structures by protectingthem before high impact periods. Likewise, corrosioncontrol strategies may also be based on the intensity andduration of multiyear climate cycles, although furtherevidence is necessary to corroborate the link betweenthese cycles and periods of accelerated corrosion.

Future studies should corroborate the results forother types of concrete, under different microclimaticconditions, as well as incorporate other effects such asdifferent curing times. The authors expect that theobserved multiyear cycles may be relevant for otherfields of study, such as ecology, agriculture and healthsciences. Such cycles may help explain the degree ofimpact and risks associated to GCC as well as theconsequences GCC has for natural and modifiedecosystems and human health.

The authors conclude that chloride concentration,which is largely associated to concrete durability, isdriven not only by seasonal atmospheric fluctuations butalso describes a pattern of multiyear cycles potentiallydriven by additional factors. Moreover, chloride con-centration levels will also be affected by GCC effectssuch as greater rainfall or humidity and greater tem-peratures. Based on this, any type of damage caused bythe environment on concrete structures should considervariation at two time scales: seasonal climate patternsthroughout the year as well as long term patterns such asmultiyear cycles. Future studies should consider bothtime scales and measure their contribution to concretedurability and, in this way, develop more precise modelsof concrete structure service life or life cycle. In this way,structure service life should be defined38 and modelledusing different stages in order to provide a more holisticway of analysing, which factors influence concretestructure durability.39,40

ConclusionsBased on results for atmospheric data and chlorideconcentration, the authors present the following con-clusions, which apply to the microclimatic conditions atthe study site, as well as materials and fabricationmethod used.

1. Temperature, rainfall, relative humidity and eva-poration recorded for the studied microclimate allshowed a well defined tendency to increase throughoutthe 40-year sampling period.

2. Maximum and mean temperature increased gra-dually throughout the sampling period, at a rate of 1and 0?22uC per decade respectively. This contrasts therate of increase reported in the IPCC (0?13uC perdecade) as well as in other international reports.

3. A pattern of multiyear cycles was described formaximum temperature values and may be controlled byfactors other than local atmospheric conditions. For

example, multiyear cycles seem to coincide recently withperiods of greater sunspot activity.

4. Maximum temperature values also exhibitedannual cycles driven by atmospheric conditions, andeach season had cycles of particular intensity.

5. The increase in maximum temperature values dur-ing recent decades, considering maximum values foreach multiyear cycle, exhibited a marked linear ten-dency, which may serve to generate future predictionsand take adequate measures to mitigate and control thepotential impacts of GCC on human activities. Based onthe observed tendency, the increase in temperature from2010 to 2030 will be of 2uC for the study site.

6. The concentration of chlorides in the studiedconcrete structures is not only affected by the typicalseasonal behaviour of climatic variables but also by longterm multiyear cycles and GCC effects such as warming.

7. Any type of damage on concrete infrastructure dueto environmental effects should consider not only shortterm seasonal effects but also long term patterns such asmultiannual cycles, which could dictate the rate of lossof concrete durability. Further information should begenerated and made available to determine which timescale better serves to explain changes in concretedurability and predict concrete structure service lifeand life cycle.

8. Concrete service life should be defined andmodelled by stages using both short and long termscales in order to determine which factors and at whichscale have a greater influence on structure durability.

Future work and recommendationsResults from this study have shown that climate effectson concrete structures may be divided into two com-ponents: those which occur between seasons within ayear and due to local atmospheric changes and thosewhich are due to long term patterns driven by extrinsicfactors characterised by multiyear cycles and GCCeffects such as warming. Until now, the literature onclimate effects on concrete structures had only paidattention to the first (short term, seasonal effects), andeven in this case, considerable error existed when pre-dicting structure service life. Considering that anadditional pattern of multiyear cycles emerged fromthe results, the authors propose the following recom-mendations for future studies.

1. When trying to predict any service life variable forconcrete structures, both long and short term patterns ofvariation should be considered.

2. Analyse if certain variables associated to structuredurability, such as reinforcement corrosion, are stronglyinfluenced by long term effects, particularly those takingplace due to GCC.

3. Discuss, based on long term patterns of variation,possible intervention strategies which take advantage oflow impact periods (characterised by low chloride con-centrations) to protect concrete structures and increasetheir durability.

4. Determine which level of variation in climaticparameters (seasonal or multiyear) has a greatercontribution to concrete structure durability.

5. Validate the existence of the long term patternobserved in this study by gathering more climatic datafor other regions and microclimates.



6. Generate standards which consider the impact ofGCC on infrastructure so that appropriate design,rehabilitation and prevention strategies are taken intoaccount and made obligatory.

7. Generate models of concrete infrastructure servicelife which take into account climate variation at dif-ferent temporal scales.

Acknowledgements

The authors acknowledge to CONACYT (ProjectsCiencia Basica 57420 and CIAM 54826) for the partiallysupport of this work and to Centro Metereologico de laComision Nacional del Agua (Meteorological Center ofthe National Water Commission) for provide theclimatic data. The authors also acknowledge Ing.Mercedes Balancan for her support in the chemicaland electrochemical test.

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