Abstract
A large amount of CO2 is emitted in a cement manufacturing process.The CO2 curing is the one of the ways to use CO2 gas[1-3].Reacting early age concrete with CO2 gas in a chamber increases its strength development.The propose of this study is a quantitative measurement on the efficiency of CO2 curing.
Table 1 shows the mix proportions of the cementitious materials.The mixtures were fabricated in two methods:(1)Compacting and(2)a general procedure to make mortar samples,following ASTM C109.The compacting method was applied for dry mix samples proportioned by a low water cement ratio(W/C):Paste(W/C=0.15)and Mortar(W/C=0.35).The dimension of the paste and mortar compacts was 40 mm cube.The dimensions for the samples,Paste(W/C=0.4)and Mortar(W/C=0.5),produced by a general procedure were 25,the size ef fect of CO2 curing[4-6].The 40,and 50 mm cube in order to analyze sealed curing for the premature sample in a mold was proceeded for 24 h at 25℃approximately.
Table 1 Mix proportions of samples
We considered two conditions for CO2 curing.The first consideration for CO2 curing is following that.The samples in a pressure vessel were subjected to 99.9%purified CO2 gas for 3 hours.Each sample in Table 1 was subjected to 350 kPa-CO2 curing for 3 hours,and the successive curing was followed:21 hmoisture curing for Paste(W/C=0.15)and Mortar(W/C=0.35)while 28 daywater curing for Paste(W/C=0.4)and Mortar(W/C=0.5).Moisture curing was conducted under relative humidity(RH)of(85±5)% and temperature of 25℃approximately,and water curing was under 23℃approximately.The other CO2 curing was at 20%concentration of CO2 where RH was(75±5)%and temperature was 25℃.Each sample was placed in a controlled chamber,and the 20% CO2 curing continued for 28 days.The control samples were also produced by moisture curing for Paste(W/C=0.15)and Mortar(W/C=0.35).The moisture curing was at(85±5)% RH and 25℃.Those for Paste(W/C=0.4)and Mortar(W/C=0.5)took water curing at 23℃.The conditions for the control curing were the same with the successive curing after 350 k Pa-CO2 curing.
Internal temperature and pressure in a pressure vessel were monitored.Pressure loss in the pressure vessel(for 350 kPa-CO2 curing)was monitored using a pressure digital gauge.The compressive strength of the samples was measured in accordance with ASTM C109.
The CO2 pressure in the pressure vessel decreased over time,where the initial pressure was approximately 350 k Pa as injected.Taking the slope at each point evaluated the carbonation rate in a unit of k Pa/h.The consumed CO2 on CO2 curing was possibly calculated with the ideal gas equation.The carbonation rate in the pressure vessel was then given by n=PV/RT in a unit of mol/h.Normalizing the carbonation rate with the cement mass required for producing the samples in the pressure vessel gave its value per cement mass in a unit of mol/(h·g).The carbonation rate was curve-fitted in a power-law function.Note that the period of 350 k Pa-CO2 curing was assigned by taking the time to get a convergence on the carbonation rate.Integrating the carbonation rate gave CO2 uptake.(https://www.daowen.com)
Figure 1 shows the CO2 uptake of the other samples.Paste(W/C=0.15)and Mortar(W/C=0.35)had a higher CO2 uptake compared to Paste(W/C=0.4)and Mortar(W/C=0.5).CO2 uptake had the effect of specimen size.Cement paste samples show that CO2 uptake increased with specimen size.
Figure 1 CO2 uptake
Figure 2 shows the strength development of Mortar(W/C=0.5)by size of specimen,where each trend was fitted in a hyperbolic equation.The 20% CO2 curing provided a higher strength gains of all samples than other curing conditions.
Figure 2 Strength-time curve of Mortar(W/C=0.5)