THE INFLUENCE OF A DRY, HOT CLIMATE ON THE RHEOLOGICAL PROPERTIES OF CONCRETE MIXTURES BASED ON LOW-WATER-CONSUMPTION CEMENTS

Аннотация

Исследуется влияние экстремальных климатических условий (высоких температур и низкой влажности) на подвижность, сохраняемость, скорость схватывания и испарение влаги в бетонных смесях. Установлены закономерности изменения реологических параметров в условиях жаркого климата. Даны рекомендации по адаптациисмесей дляжарких регионов. Ключевые слова: бетонная смесь, реотехнологические свойства, сухой климат, жаркий климат,подвижность,сохраняемость. The dry, hot climate is typical for many regions of Central Asia and the Middle East. The main climatic features are high air temperature (over 35-40 °C) and low relative humidity (<30%). Under such conditions, the rate of evaporation of moisture from the concrete mixture increases sharply, which leads to a deterioration in its technological properties, a decrease in the strength anddurability ofstructures. Cements of low water consumption (LW) have the ability to form concrete with less mixing water, which improves the water-cement ratio and allows for high strength. However, in a dry climate, the efficiency of the central heating system can also be reduced due to premature evaporationof moistureandaccelerated setting. The purpose of this study is to analyze the influence of climatic factors on the rheotechnological characteristics of CNG-based concrete mixtures and to develop recommendations forimprovingtheir resistance toexternal climaticinfluences. Research methodology. Assumethefollowing initial conditions: Airtemperature: +40 °C; Relativehumidity: 20 %; Cement:PC 500-D0 with lowwater consumption; In/Out:0.35; Additive:superplasticizer 1%byweight ofcement; Initialmobility: 22cm (according to thedraft of thecone); 544 INTERNATIONAL MULTIDISCIPLINARY JOURNAL FOR RESEARCH & DEVELOPMENT SJIF2019:5.2222020:5.5522021:5.6372022:5.4792023:6.5632024:7,805 eISSN:2394-6334 https://www.ijmrd.in/index.php/imjrd Volume12,issue06(2025) Weight ofonebatch: 20kg 1.Mobility oftheconcretemix (cone sediment) =22cm. According to experience, at a temperature of +40 °C and 20% humidity, mobility decreases by ~30%in thefirst 30minutes dueto moistureevaporation and theonset of hydration. Mobility along thecone sediment Table1 Time Expected mobility (cone draft), cm 0min 22 30min 15,4(−30%) 60min 10,5(−52%) 90min 6,6(−70%) Weconsider theretention coefficient as theratio ofmobility to theinitialone: R = r St S0 ​ Время St(см) R r 30мин 15,4 0,70 60мин 10,5 0,48 90мин 6,6 0,30 The beginning and end of setting (according to the Vic device). Standard value (GOST 310.3– 76forPC): Start:noearlierthan 45minutes End:nolater than 600min At atemperatureof +40 °C, hydration accelerates: Settingtime:t = t −Δt ≈ 90-25=65min h n0 climate End ofgrasping: tk=180-40 = 140min The loss of water due to evaporation (by weight) is determined by the following formula (SNiP 3.03.01-87): 545 INTERNATIONAL MULTIDISCIPLINARY JOURNAL FOR RESEARCH & DEVELOPMENT SJIF2019:5.2222020:5.5522021:5.6372022:5.4792023:6.5632024:7,805 eISSN:2394-6334 https://www.ijmrd.in/index.php/imjrd Volume12,issue06(2025) ΔW=E⋅ A⋅ t Here: E—evaporation rate (g/m2·h): at +40°C and 20%humidity ≈ 250g/m2·h A—open area: 0.1m2(for thetray) t—time, hour In 1hour: ΔW=250 *0,1*1=25gwater Fora mixtureweighing 20kgwith amoisturecontent of7%(1400 gof water): (that is, almost 2%ofwater is lost in onehour.). 25 1400∗100% = 1,79% Conclusion. In a dry, hot climate, concrete mixtures based on cements with low water consumption are subject to rapid evaporation of moisture and accelerated setting, which requires adjustments to the composition and concreting technology. The use of modern chemical additives, technological techniques and protective measures makes it possible to effectively adapt such mixtures to extreme climatic conditions and ensure high quality and durabilityof concrete. Listof literature: 1.GOST 10181-2014.Concrete mixes. Test methods. Moscow: Standartinform, 2015. 2. Sheindlin A.E., Gusev V.F. Influence of temperature on the structure and properties of cement stone// Building materials. 2020.No.5. 3.Rashitov K.M., Juraev S.B. Technological aspects of concreting in a hotclimate // Bulletin of ConstructionScience. –2021. 546 INTERNATIONAL MULTIDISCIPLINARY JOURNAL FOR RESEARCH & DEVELOPMENT SJIF2019:5.2222020:5.5522021:5.6372022:5.4792023:6.5632024:7,805 eISSN:2394-6334 https://www.ijmrd.in/index.php/imjrd Volume12,issue06(2025) 4.NevilleA.M. Properties ofconcrete. London: Pearson Education, 2011. 5.AISI 305 R20. Aguide to concreting in hot weather. –American InstituteofConcrete, 2020. 6.GOST 7473-2010.Concrete mixes. Technical specifications. 7.SNiP3.03.01-87.Load-bearing and enclosing structures. 8.AVI305R20.Aguide to concreting in hot weather. 547