Cold Regions Science and Technology 89 (2013) 30–35

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Cold Regions Science and Technology

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The influence of calcium nitrate as antifreeze admixture on thecompressive strength of concrete exposed to low temperatures

Fatma Karagöl a, Ramazan Demirboğa a,b, Mehmet Akif Kaygusuz c,Mehrzad Mohabbi Yadollahi a, Rıza Polat a,⁎a Department of Civil Engineering, Atatürk University, 25240, Erzurum, Turkeyb University Putra Malaysia, Engineering Faculty, Civil Engineering Department, Selangor, Malaysiac State Hydraulic Works, 8th Regional Directorate, 25100, Erzurum, Turkey

⁎ Corresponding author. Tel.: +90 5545690564; fax:E-mail address: rizapolat@atauni.edu.tr (R. Polat).

0165-232X/$ – see front matter © 2013 Elsevier B.V. Alhttp://dx.doi.org/10.1016/j.coldregions.2013.02.001

a b s t r a c t

a r t i c l e i n f o

Article history:Received 2 January 2012Accepted 4 February 2013

Keywords:Calcium nitrateConcrete compressive strengthCold weather concretingAntifreeze admixture

Based on ACI 306R-10, the minimum temperature necessary for maintaining concrete hydration and strengthgaining is 5 °C. If the weather becomes lower than 5 °C, some special measures should be taken in order toprevent decrease in the rate of hydration and to prevent fresh concrete from freezing. Most of the cold weath-er living countries spend annually plenty of money in order to facilitate concrete placing in the cold weatherand to extend the construction season. It has been investigated that the behavior of fresh and hardened con-crete contained calcium nitrate at different curing temperatures below freezing temperature of water andcompare the results with the both control samples. For this reason, calcium nitrate is used at level of 6% byweight of cement dosage in mixes. After casting, one group of samples was cured in the different deepfreezesat −5 °C, −10 °C, −15 °C, and −20 °C for 7, 14 and 28 days, and then the same samples were cured inwater at (23±1.7)°C for 7, 14, and 28 days. Calcium nitrate increased the compressive strength of concretebetween 48–964, 50–721, 29–393 and 24–183%, for −5 °C,−10 °C, −15 °C and−20 °C, respectively, whencompared to mixes without antifreeze admixtures. The results showed that it is possible to use calcium ni-trate as an antifreeze admixture in concrete technology in cold weather concreting without additionalprecautions.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Concrete is the backbone of modern construction. Cold weather isdefined as a period when the average daily temperature falls below4 °C for more than three successive days. These conditions requirespecial precautions during placing, finishing and curing. As the tem-perature decreases, concrete sets more slowly, takes longer time tofinish and gains strength less rapidly. If plastic concrete freezes, itspotential strength will be reduced by more than 50% and its durabilitywill be adversely affected (Concrete in Practice NRMCA (NationalReady Mix Concrete Association), 1998). Concrete exposed to tem-perature cycles, where water freezes to ice and ice melts to water inwinter, is deteriorated due to freezing and thawing (Polat et al.,2010).

Concrete should be protected from freezing until it attains a mini-mum compressive strength of 3.5 MPa according to ACI 306R-10 (ACICommittee 306 and ACI 306R-10, 2010). Today many admixturesare used in concrete, to protect it from freezing. These admixturesallow concrete to gain strength and setting when the air temperatureis below freezing (Korhonen, 2002a). They protect concrete by

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accelerating cement hydration. Consequently, when the weather tem-perature decreases, special precautions should be taken and using of an-tifreeze admixtures is an important method. Antifreeze admixtures arechemicals which are added to the mixing water of concrete in order tolower the freezing point of the aqueous solution. They have been usedeven at temperatures as low as−30 °C. The admixtures such as calciumchloride, calcium nitrite and calcium nitrate that contain the samecations as C3S and C2S accelerate hydration by nucleating action ofsuch ions and these result in an intensification of the processes of crys-tallization of hydrate (Ramachandran, 1995).

During the hydration of C3S, calcium hydroxide is formed which iscapable of reacting with most of the antifreezing admixtures with theformation of hydroxysalts. The hydrolyzing salts not only change theionic strength of the solution but also change the pH. Thus salts pro-mote densification of cement phase and change its microstructureand physical characteristics of concrete. The calcium hydroxynitratewas composed of calcium nitrate, water and calcium hydroxide. Thiscalcium hydroxynitrate was a double and basic salt form as well asshape needle crystals. The double and basic salts are able to formthe initial structural skeleton and function as a micro reinforcementfor the hydrosilicate matrix of the cement phase. The main cause forthe higher strength development in specimens with antifreeze ad-mixtures is the formation of an initial structural skeleton which

Table 1Physical properties of portland cement.

CEM I 42.5(Ordinary portland cement)

Results TS EN 197/1 Standard data

(min) (max)

2 days compressive strength, (N/mm2) 27.9 20.0 –

7 days compressive strength, (N/mm2) 44.928 days compressive strength, (N/mm2) 55.9 42.5 62.5Initial set time, (minute) 170 60 –

Final set time (minute) 230Volume expansion, (mm) 1 – 10Specific surface, (cm2/g) 3285 – –

Specific gravity 3.17

31F. Karagöl et al. / Cold Regions Science and Technology 89 (2013) 30–35

becomes enveloped by calcium hydrosilicates. Observations showthat a considerable amount of hydration occurs in forming the initialskeleton structure and, thereafter, even small amounts of the hy-drates forming on the skeleton give comparatively larger strengths(Ramachandran, 1995).

Chemical admixtures can extend the temperature range at whichconcrete can be placed (U.S., 2003). These chemicals prevent thewater in the mix from becoming solid ice and expanding in the spacesbetween aggregate particles before the critical hardness is reached.With their addition the concrete can be cured (Anon., 2002). The cal-cium nitrate is commonly used for this aim. This antifreeze admixturespeeds up the normal process of hydration. Its advantage in the coldweather is the concrete immune to frost damage (Korhonen andOrchino, 2001). Furthermore Victor B Ratinove et al. reported thatcalcium nitrate has been used and classified as an antifreeze admix-ture and RILEM also recommended calcium nitrate as an antifreezeadmixture (Korhonen, 2003; Ramachandran, 1995).

Two main purposes for cold weather concreting with portland ce-ment are intended. One is an adequate temperature to cure the con-crete and the other is protecting the concrete from freezing withoutthe thermal protection such as foam sheets, mineral wool or cellulosefibers, insulating, housing, covering or heating newly placed concrete.

The purposes of using calcium nitrate and the advantages resultingfrom the use of this admixture are decreasing time setting and/or an in-creasing early strength development (Myrdal, 2007).

The benefits of a reduced setting timemay include; earlierfinishing ofsurfaces and reducing of hydraulic pressure on forms. The benefits of anincrease in the early strength may include; earlier removal of forms, re-duction of the required period of curing and protection, and earlier place-ment in service of a structure or a repair (Rixom and Mailvaganam,1999). Partial or complete compensation for the effects of low tempera-tures on strength development may be prevented (Popovics, 1992).

Besides, in Europe, calciumnitrate has replaced calciumchloride as asetting accelerator. Although calcium chloride is the best accelerator, itis not a good option to severe corrosion hazards in steel reinforced con-crete. Ramachandran found that Ca(NO3)2 acted as an accelerator of set-ting in cement paste at low concentrations (Ramachandran, 1972).Accordingly, calcium nitrate is a multifunctional admixture for concrete(Popovics, 1992). Today, most suppliers of concrete admixtures offercalcium nitrate based accelerators (Justnes, 2007).

The effectiveness of an admixture depends upon such factors suchas the type and amount of cement, water content, aggregate shape,gradation and proportions, mixing time, slump, and the temperatureof the concrete.

Based on ACI 306R-10, the minimum temperature necessary formaintaining concrete hydration and strength gaining is 5 °C. If theweather becomes lower than 5 °C, some special measures should betaken in order to prevent a decrease in the rate of hydration and toprevent fresh concrete from freezing. Most of the cold weather livingcountries spend annually plenty of money in order to facilitate con-crete placing in the cold weather and to extend the construction sea-son. Besides above precautions, using antifreeze admixture is analternative without additional protection measures. However, the ef-fects of calcium nitrate on the different freezing period of concrete arenot well known. The influence of calcium nitrate on the differentperiods of the freezing and subsequently different water curingperiods should be studied. In addition, a little attention was alsotaken in previous studies that (below 0 °C) without any additionalprotection method, calcium nitrate is able to prevent the reductionof the compressive strength of concrete, when compared to the con-trol sample.

For these reasons, in the study, fresh and hardened concretescontained calcium nitrate at different curing temperatures belowfreezing temperature (−5, −10, −15 and −20 °C) and durations(7, 14 and 28 days) of water compare to the results of control sam-ples. Higher dosage of calcium nitrate could accelerate the setting of

the concrete to prevent consolidation and increase the cost. Thenthe moderate ratio of calcium nitrate is 6% by weight of cementdosage of concrete that has been chosen. After casting, each groupof concrete samples was cured in the different deepfreezes at −5,−10, −15, and −20 °C for 7, 14 and 28 days, and then the samesamples were cured in water for 7, 14, 28 days and tested in accor-dance with ASTM C 39.

2. Materials and methods

ASTM Type I portland cement (CEM I 42.5 R) and tap water wereused for all mixtures throughout the study. Physical properties andchemical composition of portland cement are shown in Tables 1 and 2,respectively. Calcium nitrate antifreeze originated from Tekkim KimyaSan. ve Tic. Ltd. Şti was used. The chemical properties of the calcium ni-trate are given in Table 3.

Aggregate with a maximum nominal size of 16.0 mm was usedas the coarse aggregates. The fine aggregate was natural sand fromErzurum/Aşkale region. The coarse and fine aggregates were separat-ed into different size fractions (0–2, 2–4, 4–8, 8–16 mm) andrecombined (30%, 15%, 20%, 35% by volume of total aggregate for0–2, 2–4, 4–8, 8–16 mm size, respectively) to a specified grading asshown in Fig. 1. The specific gravity of 0–2, 2–4, 4–8, 8–16 mm was2.40, 2.47, 2.54 and 2.63, respectively. Super plasticizer agent wasused 0.5% of cement weight for all mixtures (Korhonen, 2002b) be-cause the purpose of this study was to investigate the effects of thecalcium nitrate alone. So the concrete mixture was not air entrained.The region where the study has been done is very cold and duringnight the temperature is below−20 °C for long period (approximately40–60 days). Then the study temperature was very low such as−20 °C.

The concrete mix proportions are given in Table 4. The samewater-to-cement ratio for the controlmixtures and calciumnitratemix-tures was selected to be 0.40. In cold weather concreting practices thedosage of the cement changes between 350 and 500 kg/m3. Howeverhigher dosages such as 450 and 500 kg/m3 associate durability prob-lems such as shrinkage. Thus we preferred 400 kg/m3 which are higherthan that of normal concrete. The admixture calcium nitrate wasdissolved in the mix water. At first the dry mixture of cement, fineand coarse aggregate was added in a laboratory counter-current mixerfor 1.5–2 min. Then the calcium nitrate solution for concrete mixtureswith calcium nitrate and mixed water for concrete mixtures withoutcalcium nitrate were added into the mixer. The fresh concrete mixtureswith andwithout calciumnitrate admixtureweremixed in a laboratorycounter-current mixer for a total of 5 min and were cast into100×200-mm cylinder plastic molds from each mixture. The cylinderswere consolidated with needle vibrator until homogenous specimenwas achieved. After casting, the concrete mixtures in plastic state to-gether withmoldswere immediately transferred to the automatic tem-perature control deepfreezes at −5 °C, −10 °C, −15 °C and −20 °Cfor 7, 14, and 28 days. The temperatures of deepfreezes were calibrated

Table 2Chemical properties of portland cement.

Results TS EN 197/1Standard data(max)

Heating loss (%) 2.03 5.00Insoluble matter (%) 0.25 5.00Cl2 (%) 0.0102 0.10SiO2 (%) 20.54 –

Al2O3 (%) 5.12 –

Fe2O3 (%) 3.69 –

CaO (%) 62.98 –

MgO (%) 1.70 –

SO3 (%) 2.88 –

Main constituent (%)

C3S 53.2C2S 16.7C3A 7.6C4AF 10.7

Fig. 1. Grain-size distribution curve.

Table 4

32 F. Karagöl et al. / Cold Regions Science and Technology 89 (2013) 30–35

before casting. There was no connection to the external environment.There was enough space to provide air circulation between samples.The temperatures of the deepfreezes weremonitored. The temperatureof deepfreeze did not increase significantly when a number of speci-mens were added to the chamber to cure. When the temperature ofthe environmental chamber decreases the deepfreeze automaticallyattained same initial temperature. Calciumnitrate groupswere denotedby S1, S2 and S3 for 7, 14 and 28 days deepfreeze curing and 7, 14 and28 days for additional lime saturated water curing (23±1.7)°C S1; S2;and S3 were denoted by S1*, S1** and S1***; S2*, S2** and S2***, S3*,S3** and S3***, respectively. Control samples were denoted by C1; C2;and C3 for 7, 14 and 28 days of deepfreeze curing durations and 7, 14and 28 days for additional lime saturated water curing (23±1.7)°CC1; C2; and C3 were denoted by C1*, C1** and C1***; C2*, C2** andC2***; and C3*, C3** and C3***, respectively. Samples contain 6% calciumnitrate and control samples were only 7 days stored in water curing(23±1.7)°C in accordance with ASTM C 192 and were denoted bySW7 and CW7, respectively (ASTM C192/C192M–12, 2012). Beforethe specimens placed in the lime water bath in accordance with ASTMC 192, they were located in room temperature through a day and thenthey were stripped out of the molds.

Before compressive strength testing, samples were kept in roomtemperature for 24 h and then the cylinders were capped with an ap-propriate material such as sulfur prior to compressive strength test toprevent inaccurate strength results. According to ASTM C 39 the com-pressive strength of hardened concrete is determined from compres-sion tests on standard cylindrical specimens. Compressive strengthtests are used during concrete mix design to evaluate the perfor-mance of the materials and to establish mixture proportions thatwill give the required strength. “Compressive strength” is defined asthe average of the strengths of all cylinders of the same age madefrom a sample taken from a single batch of concrete. At least two

Table 3Chemical properties of calcium nitrate (Ca(NO3)2. 4H2O %98 pure).

Chemical properties Approx values

Chloride (Cl) ≤0.05%Sulfate (SO4) ≤0.5%Heavy metal (Pb) ≤0.005%Ferrite (Fe) ≤0.05%pH 5–7Solubility in water 1470 g/lMelting point 45 °C

cylinders, or preferably three, are required to constitute a test(ASTM C39/C39M–12a, 2012). In this study, compressive strengthsof three samples from each curing condition were determined foreach group. Result from control samples and calcium nitrate sampleswas compared for the same curing conditions.

3. Results and discussion

The results are given in Tables 5–7. They are evaluated anddiscussed below.

3.1. Workability

The properties of freshly mixed concrete were determined byslump. The slump test is an empirical test that measures the work-ability of fresh concrete. The slump test is used to ensure uniformityfor different batches of similar concrete. Cold weather concretingcalls for a lower slump. This is desirable because it will have lessbleed water on the surface. If excess bleed water blended into theconcrete during trowelling, surface strength will be lowered resultingin freeze low damage (Evan, 2008). According to ASTM C 143 the testis carried out using a mold known as a slump cone or Abrams cone.The cone is placed on a hard non-absorbent surface. This cone is filledwith fresh concrete in three stages, each time it is tamped using a rodof standard dimensions. At the end of the third stage, concrete isstruck off flush to the top of the mold. The mold is carefully lifted ver-tically upwards, so as not to disturb the concrete cone. Level of con-crete subsides. This subsidence is termed as slump (ASTM C143/C143M–10a, 2010). The average slump of different control mixturewas 4 cm. The average slump flow of the 6% calcium nitrate was6 cm, which showed reasonably good flow ability. Slump of calciumnitrate's sample was higher than that of control. The main reason isthat 6% calcium nitrate behaved as a super plasticizer and increasedthe workability of the mixture.

The mixture proportions for 1 m3 concrete.

Materials Control mixture Antifreeze mixture

Ratio of admixture (%) 0 6%w/c ratio 0.40 0.40Cement (kg) 400 400Calcium nitrate (kg) – 24Water (kg) 160 160Super plasticizing agent (%) 0.5 0.5Air 0.02 –

Natural aggregate (kg) 0–2 mm 498 4872–4 mm 256 2514–8 mm 352 3448–16 mm 638 625

Table 5Compressive strength test results for 7 days in deepfreeze curing and 0, 7, 14 and 28 days in water curing.

Temperature (°C) 7 days deepfreezecure (MPa)

7 days freezercure+7 days watercure (MPa)

7 days freezercure+14 days watercure (MPa)

7 days freezercure+28 days watercure (MPa)

Only 7 days watercure (MPa)

S1 C1 S1* C1* S1** C1** S1*** C1***

−5 35.93 7.92 44.69 29.63 38.71 13.91 38.69 26.18 Control water(CW7)37.96

−10 18.23 7.81 24.51 10.41 21.27 9.63 35.30 17.85−15 16.10 6.97 15.58 10.65 17.26 9.82 35.28 16.42−20 15.53 6.55 11.68 12.42 14.35 9.81 33.26 15.10 Calcium nitrate water

(SW7)45.95

S1: denotes samples contain 6% calcium nitrate and 7 days stored in deepfreeze.C1: denotes control samples 7 days stored in deepfreeze.S1*: denotes samples containing 6% calcium nitrate and 7 days stored in deepfreeze+7 days in water curing.C1*: denotes control samples 7 days stored in deepfreeze+7 days in water curing.S1**: denotes samples containing 6% calcium nitrate and 7 days stored in deepfreeze+14 days in water curing.C1**: denotes control samples 7 days in deepfreeze+14 days in water curing.S1***: denotes samples containing 6% calcium nitrate and 7 days stored in deepfreeze+28 days in water curing.C1***: denotes control samples 7 days stored in deepfreeze+28 days in water curing.SW7: denotes samples containing 6% calcium nitrate 7 days in water curing.CW7: denotes control samples 7 days in water curing.

33F. Karagöl et al. / Cold Regions Science and Technology 89 (2013) 30–35

3.2. Compressive strength

The effect of calcium nitrate as an antifreeze admixture on thecompressive strength of concrete was given in Tables 5–7. Resultsare discussed as below:

3.2.1. Compressive strength after 7 days in deepfreeze curing and 0, 7, 14and 28 days in water curing

After frozen period samples were kept 24 h in room temperatureprior to tests. Thus probability of frozen samples was eliminated be-fore testing compressive strength.

Table 5 shows that the compressive strengths of S1 sampleschanged between 15.53 and 35.93 MPa for −5, −10, −15, and−20 °C temperatures. However, compressive strengths of C1were between 6.55 and 7.92 MPa for the same temperature range.Variation in the C1 group due to the decreasing of the deepfreezetemperature was negligible. This showed that after −5 °C, hydrationof cement stopped and it does not matter whether the temperature is−10 °C or −20 °C. Reduction in C1 when compared to CW7 wasaround 80% for −5 °C.

Adding 6% calcium nitrate caused an increment in the compres-sive strength of about 353, 133, 130, and 137% for −5 °C, −10 °C,−15 °C, and −20 °C temperatures, respectively, when compared tothe compressive strength of control sample that was exposed to thesame conditions. The highest compressive strength was observed forS1*whichwas 44.69 MPa and itwas 18% higher than that of CW7. How-ever, with the decreasing of the deepfreeze temperature, the effects ofthe calcium nitrate also decreased. At the same time additional watercuring, especially 28 dayswater curing duration, increased all compres-sive strength samples above 30 MPawhich is a compressive strength of

Table 6Compressive strength test results for 14 days in deepfreeze curing and 0, 7, 14 and 28 days

Temperature (°C) 14 days freezer cure(MPa)

14 days freezer cure+7 dwater cure(MPa)

S2 C2 S2* C2

−5 26.30 7.56 35.75 18−10 24.22 3.42 16.86 8−15 16.31 4.02 16.01 9−20 6.54 3.67 15.99 9

structural concrete, even though samples exposed to −20 °C passedthis limit after 28 days water curing.

S1* sample at −5 °C reached 87% of the 28 days compressivestrength of CW28 sample at 7 days deepfreeze plus 7 days water cur-ing. This strength is higher than that of control sample exposed to thesame temperature. For the same conditions the control sample's com-pressive strength was 57% of CW28 sample.

For 7 days deepfreeze curing plus 14 days water curing C1** sam-ples showed approximately the same compressive strength at allrange of the freezing temperatures. These compressive strengthswere changed between 9.63 and 13.91 MPa. The maximum compres-sive strength was observe at −5 °C for S1** samples and was38.71 MPa. The main factor to design the strength of concrete is com-monly the compressive strength of the 28th days (Popovics, 1992).Calcium nitrate showed very good performance at all level of belowfreezing temperatures that they exposed. The compressive strengthof S1** was higher than CW7 sample. Calcium nitrate samplesobtained 38.71, 21.27, 17.26 and 14.35 MPa compressive strengthfor −5, −10, −15, and −20 °C, respectively.

For 7 days deepfreeze curing plus 28 days water curing thecompressive strengths of C1*** samples were in the range of15.10–26.18 MPa for −5, −10, −15, and −20 °C temperatures.For the same temperature range the compressive strengths of S1***samples were in the range of 33.26–38.69 MPa for −5, −10, −15,and −20 °C temperatures.

After 7 days deepfreeze curing duration, the relative strength in-crement by 28 days water curing for S1*** samples was 8, 93, 119and 114% for −5, −10, −15, and −20 °C when compared to the S1samples, respectively. The highest compressive strength was38.69 MPa at −5 °C for S1*** samples.

in water curing.

ays 14 days freezer cure+14 dayswater cure(MPa)

14 days freezer cure+28days water cure(MPa)

* S2** C2** S2*** C2***

.19 24.25 14.02 55.17 23.80

.29 17.91 11.90 48.34 19.09

.38 17.03 11.55 37.56 16.84

.99 17.05 11.86 34.36 14.03

Table 7Compressive strength test results for 28 days in deepfreeze curing and 0, 7, 14 and 28 days in water curing.

Temperature (°C) 28 days freezercure (MPa)

28 days freezercure+7 days watercure (MPa)

28 days freezercure+14 days watercure (MPa)

28 days freezercure+28 days watercure (MPa)

Only 28 days watercure (MPa)

S3 C3 S3* C3* S3** C3** S3*** C3***

−5 33.21 3.12 32.29 31.41 29.10 30.46 57.51 21.92 Control water(CW28)51.40

−10 10.76 1.31 17.02 11.32 20.01 12.55 52.93 19.60−15 5.35 0.88 16.59 10.50 17.28 13.35 51.35 14.15−20 4.13 0 14.90 10.64 15.94 12.84 47.02 16.61 Calcium nitrate water

(SW28)46.57

34 F. Karagöl et al. / Cold Regions Science and Technology 89 (2013) 30–35

It was clear that even though calcium nitrate antifreeze was beingused, additional water curing was necessary for the development ofcompressive strength and to gain a high level of compressive strengthresults.

Antifreeze admixtures force the water within the concrete to re-main at least partially liquid until the temperature falls below the‘eutectic point’, the temperature at which no matter how much anti-freeze is added, the solution will completely freeze. The temperatureof the eutectic point varies depending on which compound is used. Assome ice crystals form at temperatures above the eutectic point, theoperating range for each mix is usually limited to temperatures; afew degrees higher than the eutectic point (Anon., 2002). The effectof the calcium nitrate on the cold weather concreting is crucial andit may preserve concrete for long time at very low temperaturesuch as −15 °C because this temperature is higher than the eutecticpoint of calcium nitrate which is −16 °C for 35% percent solution.Thus, there was no significant difference between control concreteand calcium nitrate for the −20 °C temperatures and curing time.The calcium nitrate at −20 °C is not that effective to improve thecompressive strength. However, the study is an investigation to iden-tify the behavior of the concrete below the eutectic point. Because ofthis reason the temperature below the eutectic point was studied.

For this study it is very difficult to predict the freezing point ofconcrete by eutectic point of calcium nitrate because the temperatureof the other ingredient will also affect the temperature of the mixes.Especially the hydration of the cement with water during the mixingperiod will increase the temperature of medium. The amount ofcalcium nitrate is 15% of the mixing water. Accordingly, the freezingpoint of water in the mixture was between −4.6 °C and −7.6 °C(Ramachandran, 1995). However, as the ambient temperature haschanged by the reaction of hydration of cement the freezing pointof the mixture cannot be done on a precise estimation.

Cold weather places serious constraints on concrete construction.As temperatures drop, concrete sets more slowly, takes longer to fin-ish, and gains strength less rapidly. What is needed is a concrete thatcan be placed and cured in subfreezing weather without thermalprotection. The goal in proportioning mixtures for cold weather is toachieve a concrete that cures rapidly. That is, one that sets morequickly and gains strength more rapidly than it ordinarily would(Korhonen, 2001–2003).

3.2.2. Compressive strength after 14 days in deepfreeze curing and 0, 7,14 and 28 days in water curing

It is obvious from Table 6 that with the decreases of the tempera-tures, compressive strength of the C2 was drastically decreasedand their compressive strength were 7.56, 3.42, 4.02 and 3.67 MPaat −5, −10, −15 and −20 °C temperatures, respectively. However,compressive strengths of S2 were very high when compared tothose of C2. S2's compressive strengths were also decreased withthe decreasing of deepfreeze temperatures and at −20 °C it wasaround 6.5 MPa. It can be concluded that calcium nitrate cannot con-serve concrete exposed to the −15 °C and below if it does not curedadditional water curing for 28 days. Maximum compressive strength

was observed at −5 °C and S2*** samples with 6% calcium nitrate.This strength was higher than both the compressive strength ofonly water cured control samples and 6% calcium nitrate samplesfor 28-days. Mixes without calcium nitrate gained very low strengths,even at −5 °C temperature and it was changed between 14 and 46%of the control water cured for 28 days. When the compressivestrength of calcium nitrate samples compared to the those of withoutcalcium nitrate, cured at all temperatures for all curing durations, itcan be seen that calcium nitrate increased the compressive strengthof all groups at all deepfreeze temperatures. This showed that calciumnitrate admixture accelerated cement hydration and protects thewater from freezing.

Antifreeze admixtures have two purposes: depress the freezingpoint of water and allow the water cement to hydrate at low temper-ature. The effectiveness of antifreeze for reducing the freezing pointof water is related to its eutectic point. The eutectic point is the lowesttemperature below which additional quantities of antifreeze will notdepress the freezing point further (Korhonen and Cortez, 1991).

Thus the compressive strength of concretes cured at all tempera-tures was higher than those of without calcium nitrate under thesame curing condition. At 14 days deepfreeze plus 7 days water cur-ing all control samples showed between 16 and 35% strength of28-day water cured, control samples. At the same conditions thecompressive strengths of antifreeze mixture were 35.75, 16.86,16.01 and 15.99 MPa at−5 °C,−10 °C,−15 °C and−20 °C temper-atures, respectively. These strengths were changed between 70 and31% strength of 28-day water cured control samples. The compressivestrength of S2*** was higher than CW28 sample at −5 °C. S2***sample's compressive strength was changed between 94 and 67%strength of 28-day water cured control samples at −10, −15 and−20 °C. This increment in compressive strength is due to the addi-tional water curing time. Even at −20 °C, the compressive strengthgain was 67% strength of 28-day water cured control samples. Atthe same temperatures, the control sample's compressive strengthwas 14.03 MPa while the calcium nitrate sample's compressivestrength was 34.36 MPa. Under low temperatures, concrete struc-tures suffer serious deterioration. This is due to the ice formation inconcrete micro pores, which causes micro cracking and loosens con-crete microstructure. In a cold region, concrete structures aresubjected to freezing and thawing. Concrete changes its mechanicalproperties in various aspects when it is cooled till very low tempera-ture. It is known that the change is mainly due to the freezing ofwater in concrete; since phase transition from water to ice leads toabout 9% expansion by volume, internal micro cracks are initiated inconcrete. And repetition of cooling and heating progress the deterio-ration of concrete, by continuous initiation or propagation of thecracks (Fagerlund and Setzer, 1991).

3.2.3. Compressive strength after 28 days in deepfreeze curing and 0, 7,14 and 28 days in water curing

Groups S3 and C3 were stored in deepfreeze for 28 days and thencured in water 0, 7, 14 and 28 days for additional curing periods.

35F. Karagöl et al. / Cold Regions Science and Technology 89 (2013) 30–35

The compressive strengths of S3 samples were in the range of33.21–4.13 MPa, for −5, −10, −15, and −20 °C freezer tempera-tures. Compressive strengths of control samples were between 3.12and 0 MPa for the same temperature range.

According to C3, use of calcium nitrate increased compressivestrength of samples for all temperatures. The highest compressivestrength, S3***, was 57.51 MPa at −5 °C. Adding calcium nitrate in-duced an increment in the compressive strength of about 162%(S3*** group) when compared to control samples that exposed thesame curing condition and duration (C3*** group). As it can be seenfrom Table 7 that with decreasing curing temperature the strengthof both samples those with and without calcium nitrate decreased.S3 group's compressive strength decreased drastically with decreas-ing deepfreeze temperature when compared with S1 and S2. Controlsamples also showed the same behavior. However, reductions in C1,C2, and C3 were greater than those of S1, S2 and S3. Control samples'compressive strengths were negligible and C3 did not show anystrength at−20 °C. This means that mix water immediately froze be-fore the setting of the concrete in deepfreeze. The internal stressescaused by ice formation might be released in the concrete. Thus un-frozen water in large pores transports toward smaller pores or par-tially empty pre-existing in concrete. As a result of this the internalmicro cracks are initiated in concrete. Both micro cracks and largeice voids induced reductions in compressive strengths of concrete.In this study, micro cracks those formed on the surface of concretewere observed with naked eyes. There were no any ice crystals onthe surface of the samples.

After water curing all control and calcium nitrate samples' com-pressive strength increased. The results showed that one time freez-ing of fresh concrete without calcium nitrate antifreeze inducedaround 70% loss in compressive strength for 28 days deepfreeze cur-ing plus additional 28 days water curing. It is important to state thatrevitalization by 28-day water curing after exposure up to −20 °C ispossible by calcium nitrate anti-freeze admixture. Results alsoshowed that calcium nitrate may conserve the concrete for longtime of cold weather exposure such as −20 °C temperatures withoutany external or additional protection methods and precautions be-cause succeeded normal curing condition (water curing) may beenough to vitalize the froze cement paste to gain their originalexpected compressive strength.

According to the results additional water curing is very importantfor both long term low deepfreeze curing condition and especially attemperature lower than −10 °C as indirect results of antifreeze ad-mixture which increases the strength of the concrete will enhancethe freezing-thawing resistance of concrete too.

4. Conclusions

1- Compressive strength of both control and calcium nitrate concretewas decreased with decreasing deepfreeze temperatures. Howev-er, reductions in concrete with calcium nitrate were lower thanthat of control sample.

2- Compressive strength of C1, C2 and C3 was 7.92, 7.56 and 3.12,but that of S1, S2 and S3 was 35.93, 26.30 and 33.21, respectivelyat −5 °C.

3- Calcium nitrate concrete's compressive strength was high enoughup to 14 days of exposure of−10 °C deepfreeze temperature with-out any additional precautions. However, after 28 days of deep-freeze curing it can conserve concrete that exposed to −5 °C onlywithout any protection or additional water curing.

4- In many countries after long cold weather season there is a warmand rainy season thus freezing season can be followed by rainy

season which resemble the regime of the study. For long termcold weather exposures additional water curing could vitalizecompressive strength of concrete completely.

5- The calcium nitrate affected significantly in the early age compres-sive strength. Results show that calcium nitrate is a good settingaccelerator. Desired setting time, compressive strength and otherproperties of concrete can be obtained in cold weather by addingcalcium nitrate. At the same time this additive increases the rateof hardening action, reducing time to achieve sufficient strengthto take over efforts developed by internal freezing.

Acknowledgments

This research was supported by the research project “The effect ofantifreeze admixtures on the properties of concrete casted in coldweather” (BAP Code: 2009/271) from the Atatürk University, ScientificResearch Projects (BAP) Program in Erzurum, Turkey.

References

ACI Committee 306, ACI 306R-10, 2010. Guide to Cold Weather Concreting. AmericanConcrete Institute, Detroit, Michigan.

Anon., 2002. Related technical issues. Chapter 5 Using Concrete in Freezing Tempera-tures, pp. 55–67.

ASTM C143/C143M-10a, 2010. Standard test method for slump of hydraulic cementconcrete.

ASTM C192/C192M-12, 2012. Standard practice for making and curing concrete testspecimens in the laboratory.

ASTM C39/C39M-12a, 2012. Standard test method for compressive strength of cylin-drical concrete specimens.

Concrete in Practice NRMCA (National Ready Mix Concrete Association), 1998. CIP 27cold weather concreting. Technical Information Prepared by NRMCA, pp. 1–10.

Evan, G., 2008. Cold Weather Concreting. Precast Inc. Magazine, pp. 1–7 (January-February).

Fagerlund, G., Setzer, M., 1991. Freeze-thaw and de-icing resistance of concrete. RILEMCommittee TC-117 FDC, Lund Institute of Technology Research Seminar Held inLund, pp. 1–165 (June 17).

Justnes, H., 2007. Calcium nitrate as multifunctional concrete admixture. in Slovenian14th Slovenian colloquium on Concrete, Ljubljana, Slovenia, 29th May, 2007,pp. 21–28.

Korhonen, C., 2002a. Off-the-shelf antifreeze admixtures. Technical Report TR02-07. USArmy Corps of Engineers, Engineer Research and Development Center, p. 38(April).

Korhonen, C., 2002b. Effect of high doses of chemical admixtures on the freeze thawdurability of portland cement concrete. Technical Report TR02-05, pp. 1–38(February).

Korhonen, C., 2003. “Effect of high doses of chemical admixture on strength developmentand freeze thaw durability of Portland cement mortar”, PhD theses, pp. 14–16.

Korhonen, C., 2001–2003. New Developments in Cold-Weather Concreting. ResearchCivil Engineer, U.S. Army Cold Regions Research and Engineering Laboratory, pp.1–7 (April).

Korhonen, C., Cortez, E., 1991. Antifreeze Admixtures for Cold Weather Concreting.American concrete Institute, pp. 1–4 (March).

Korhonen, C., Orchino, Sherri A., 2001. Off-the-shelf antifreeze admixtures. TechnicalReport TR-01-02. US Army Corps of Engineers, Engineer Research and DevelopmentCenter, pp. 1–23 (January).

Myrdal, Roar, 2007. Accelerating admixtures for concrete. SINTEF REPORT Building andInfrastructure Concrete and Innovation Center, Project No: 3D006020, pp. 1–35(12–05).

Polat, R., Demirboğa, R., Karakoç, M.B., Türkmen, İ., 2010. The influence of lightweightaggregate on the physico-mechanical properties of concrete exposed to freeze–thaw cycles. Cold Regions Science and Technology 60, 51–56.

Popovics, S., 1992. Concrete materials, Properties, Specifications and Testing, 2nd edition.William Andrew Publishing, Noyes, pp. 236–246 (Chapter 6).

Ramachandran, V.S., 1972. Elucidation of the role of chemical admixtures in hydratingcements by DTA technique. Thermochimica Acta 4, 343–366.

Ramachandran, V.S., 1995. Concrete Admixtures Handbook, Second edition. pp. 740–756.Rixom, R., Mailvaganam, N., 1999. Chemical Admixtures for Concrete, Chapter 6. E&FN

Spon, London, pp. 208–211.U.S., 2003. Cold Weather Concreting. U.S. Army Engineer Research and Development

Center, pp. 1–3.