# Crossover Effect in Cement-Based Materials: A Review  
[PERSON]  
1 Department of Civil Engineering, Faculty of Engineering, University of Malaya,  
Kuala Lumpur 50603, Malaysia 1  
[PERSON]  
2 Department of Building Surveying, Faculty of Built Environment, University of Malaya,  
Kuala Lumpur 50603, Malaysia 1  
[PERSON]  
1 Department of Civil Engineering, Faculty of Engineering, University of Malaya,  
Kuala Lumpur 50603, Malaysia 1  
[PERSON]  
1 Department of Civil Engineering, Faculty of Engineering, University of Malaya,  
Kuala Lumpur 50603, Malaysia 1  
[PERSON]  
1 Department of Civil Engineering, Faculty of Engineering, University of Malaya,  
Kuala Lumpur 50603, Malaysia 1  
Footnote 1: email: {hakim_1,hakim  
of concrete has the same tendency, but the variation in its value with accelerated curing temperatures is not as prominent as that of compressive strength [8]. [PERSON] et al. [9] stated that splitting tensile strength of the CBMs is more affected by the mechanism of crossover effect (COE) than compressive strength. Researchers [5; 10] described that increasing curing temperature of CBMs, such as cement pastes, mortars and concretes, increases rate of early-age strength gain but lowers the long-term strength (see Figure 1). [PERSON] and [PERSON] [11] also reported that concrete exposed to high curing temperatures exhibits accelerated hydration and non-uniform spreading of the hydration products. Such an exposure creates less porosity at early-ages and great porosity at later-ages. It results in increased compressive strength at early-ages and reduced compressive strength at later-ages [8]. [PERSON] and [PERSON] [12] described that concrete cured at elevated temperature of 38 \({}^{\circ}\)C had less porosity and more compressive strength at seven days than those cured at 20 \({}^{\circ}\)C. However, at 28-days, the porosity of elevated temperature cured concrete increased and compressive strength decreased than that of normally cured concrete. [PERSON] and [PERSON] [13] studied the effect of elevated curing temperatures up to 50 \({}^{\circ}\)C on supersulfated cements incorporating low and high alumina slags. They observed lower porosity and higher compressive strength due to elevated temperatures (38 \({}^{\circ}\)C and 50 \({}^{\circ}\)C) than the samples cured at normal temperature (23 \({}^{\circ}\)C) at the age of seven days. [PERSON] et al. [14] emphasised that under elevated temperatures, cement mortars and concretes have more porous and poorer physical structures than those developed at normal room temperature. They also stated that high temperatures increase strength gain at the early ages, whereas substantial amount of the formed hydrates have insufficient time for proper arrangement at the later ages. This process results in COE, a decrease in ultimate compressive strength of CBMs. According to the research reports [15; 16], COE may occur between seven and 10 days in Portland cements of various mineralogical compositions. [PERSON] et al. [17] stated that the initial fast hydration of Portland cement can produce a lesser homogenous microstructure that causes the COE in cements and concretes. [PERSON] et al. [18] also reported that such a process of Portland cement can decrease hydration at later ages. This decrease is due to the postponing or ending of the hydration of anhydrous cement. Moreover, the hydration products at lesser temperatures have adequate time to precipitate and diffuse homogeneously in the whole cement matrix. According to [PERSON] et al. [8], the COE of type V Portland cement concrete is not very clear compared with that of type I Portland cement concrete because of varying rates of hydration. Figure 1: Crossover effect (COE) with maturity and strength at low and high temperatures. The COE in CBMs due to accelerated initial and prolonged curing is of great concern to researchers because of the utmost importance of concrete structures in the present construction industry.