The effects of curing temperature on the physico-chemical and mechanical properties of OPC–slag mixes depend on free lime, combined slag, chemically combined water, total pore volume, compressive strength and flexural strength. Generally, the free lime contents of OPC pastes increase with curing temperature. This may be due to the increased rate of hydration with temperature, particularly at early ages. Whereas the free lime content of pozzolanic cement pastes containing WCS decreases with increase of curing temperatures. This is due to the enhancement of the pozzolanic reaction of slag as the curing temperatures increase.

The chemically combined water content increases and total pore volume decreases with curing temperature; this is due to the progress of hydration to form more hydrates. The hydration products fill up the open pores, thus increasing the bulk density and decreasing the total pore volume. Cement mixes containing slag show lower values of total pore volume and higher values of combined water in comparison with those of the plain mix at all curing temperatures. This is due to the thermal activation of slag, thus increasing the rate of pozzolanic reaction with the liberated Ca(OH)2, forming additional amounts of dense hydrates. Also, OPC–WCS mix has lower values of total pore volume and higher values of combined water than OPC–ACS mix at all curing temperatures. As the curing temperatures increase from 75 up to 100 °C values of chemically combined water decreases. This is due to the transformation of the initially formed CSH with higher combined water content, to CSH, which has a lower combined water content.

The values of compressive strength of cement mortars improved for all cement mixes cured at early ages of hydration up to 28 days with increase of temperature from 25 °C up to 100 °C. This is may be due to the acceleration of the hydration reactions. This may be due to the increased rate of hydration with temperature, particularly at early ages. The degree of hydration is controlled by the density and thickness of the calcium silicate hydrate layer around the cement grains. This layer retards hydration and, when it attains a certain thickness, it prevents further hydration during the later ages.

The elevated curing temperatures have a marked effect on the early age strength of cement mixes containing slag. This beneficial effect may be due to the acceleration of both hydration and pozzolanic reactions. At later ages of hydration, the elevated curing temperatures more than 45 °C adversely affect the compressive strength of only OPC mortars. In contrast, the elevated curing temperatures have beneficially effect on the compressive strength of OPC–slag mortars. This indicates that, the elevated temperature conditions are beneficial from the strength development perspective for pozzolanic cements. The results show beneficial effect of elevated curing temperature on the flexural strength of cement mortars containing slag at all ages of curing. Highest flexural strength of OPC–slag mortars containing WCS was obtained at curing temperature up to 100 °C. In contrast, the elevated temperature improves the early age flexural strength of OPC mortars.

At normal curing temperature WCS blended cement paste /mortar, the early strength gain is less due to pozzolonic reaction. But at elevated temperature strength gain is increases. It also depends on cement content, properties of WCS and fineness of blend.

Our studies and most others have shown that increasing temperature from say 20 to 38C have generally led to improved mechanical properties of ggbs blended mortars, particularly during the early periods of hydration.

Yes, the elevated curing temperatures have a marked effect on the early age strength of cement mixes containing slag. This beneficial effect may be due to the acceleration of both hydration and pozzolanic reactions. At later ages of hydration, the elevated curing temperatures more than 45 °C adversely affect the compressive strength of only OPC mortars. In contrast, the elevated curing temperatures have beneficially effect on the compressive strength of OPC–slag mortars. This indicates that, the elevated temperature conditions are beneficial from the strength development perspective for pozzolanic cements.

I fully agree with Saleh as we found the same trend with PLC at 38C but this beneficial effect of increased temperature in the slab blends tend to diminish from about 28days of curing. I'm not sure what happens if the temperature was much higher.

Sorry I meant OPC above not PLC please

As the curing temperature increases, the free lime contents and total pore volume of pozzolanic cement pastes decrease, whereas, the combined slag contents and chemically combined water contents increase with curing temperature, this is due to the progress of hydration to form more hydrates. The hydration products fill up the open pores, hence the compressive strength increases.

The results show also that highest values of compressive and flexural strength of pozzolanic cement mortars containing either WCS or ACS were obtained at 35–100C. The elevated temperatures improve the early age compressive and flexural strength of pozzolanic cement mortars. Whilst at later ages of hydration, OPC compressive and flexural strength decreases, especially at 45 up to 100C.

The effect of elevated curing temperature on the properties of cement mortars is vital for heat resistance. Addition of pozzolanas, such as slag, to type I cement is known to increase heat resistance. In this study, OPC was partially substituted by two types of slag (WCS and ACS) in the ratios of 10, 20, 30, 40 and 50 wt.%. The cement mortars were cured for 120 days at different curing temperature from 25 to 100C. The results show that, elevated curing temperatures improves the early age strength in the all cement mortars. Also, the results indicated that, the pozzolanic cement mortars gives higher compressive strength than the plain cement mortars, especially at curing temperatures above 35C. Therefore, slag pozzolanic cement mortars can be beneficially used in the hot conditions.

Yes, the chemically combined water content increases and total pore volume decreases with curing temperature; this is due to the progress of hydration to form more hydrates. The hydration products fill up the open pores, thus increasing the bulk density and decreasing the total pore volume. Cement mixes containing slag show lower values of total pore volume and higher values of combined water in comparison with those of the plain mix at all curing temperatures. This is due to the thermal activation of slag, thus increasing the rate of pozzolanic reaction with the liberated Ca(OH)2, forming additional amounts of dense hydrates. Also, OPC–WCS mix has lower values of total pore volume and higher values of combined water than OPC–ACS mix at all curing temperatures. As the curing temperatures increase from 75 up to 100 °C values of chemically combined water decreases. This is due to the transformation of the initially formed CSH with higher combined water content, to CSH, which has a lower combined water content.

I completely agree with that, The effects of curing temperature on the physico-chemical and mechanical properties of OPC–slag mixes depend on free lime, combined slag, chemically combined water, total pore volume, compressive strength and flexural strength. Generally, the free lime contents of OPC pastes increase with curing temperature. This may be due to the increased rate of hydration with temperature, particularly at early ages. Whereas the free lime content of pozzolanic cement pastes containing WCS decreases with increase of curing temperatures. This is due to the enhancement of the pozzolanic reaction of slag as the curing temperatures increase.

Cement mixes containing slag show lower values of total pore volume and higher values of combined water in comparison with those of the plain mix at all curing temperatures. This is due to the thermal activation of slag, thus increasing the rate of pozzolanic reaction with the liberated Ca(OH)2, forming additional amounts of dense hydrates. Also, OPC–WCS mix has lower values of total pore volume and higher values of combined water than OPC–ACS mix at all curing temperatures.