Shrinkage Behavior of Cementitious Mortars Mixed with Seawater

Abstract

The shrinkage behavior of cementitious materials mixed with seawater is investigated. Cement mortar mixtures were prepared with two water-to-cementitious materials ratios (w/cm = 0.36 and 0.45), two binder compositions (namely, ordinary portland cement (OPC) and OPC with 20 % fly ash replacement), and two types of water (tap water and seawater). The autogenous and drying shrinkage behavior of these mixtures are examined using ASTM standard test methods for 65 days. The use of seawater as mixing water increased the autogenous shrinkage. At w/cm 0.36, the ultimate autogenous shrinkage increased from 213 μs in the mixture with tap water to 387 μs in the mixture with seawater; the corresponding values were 149 and 314 μs, respectively, for mixtures with w/cm 0.45. An acceleration of the cement hydration at early ages caused by the seawater is identified as the cause of the increase in autogenous shrinkage in mixtures with seawater. At w/cm 0.36, seawater did not have a strong effect on the drying shrinkage, and tested mixtures had ultimate drying shrinkage values between 543 and 663 μs. At w/cm 0.45, in mixtures without fly ash, ultimate drying shrinkage increased from 838 μs in the mixture with tap water to 1,027 μs in the mixture with seawater. In mixtures with fly ash, the ultimate drying shrinkage increased from 738 μs in the mixture with tap water to 1,370 μs in the mixture with seawater. The drastic increase in the drying shrinkage in mixtures containing fly ash and seawater at w/cm 0.45 seems to be due to changes in mass loss behavior and the development of a finer pore size distribution. In applications where drying shrinkage may be a concern, the use of fly ash in seawater-mixed concrete could be problematic and lead to increased cracking risk. While the trends observed here will also hold in concrete, quantifying drying shrinkage and cracking of concrete based on the drying shrinkage of mortar mixtures is complex and depends on many other factors.

Effects of mixing water salinity on the properties of concrete

“…In accordance with the mechanism, capillary tension is highly related to the moisture and pore size distribution of concrete (Hansen, 1987). Therefore, the observed effect of salinity, as discussed above, is believed to be due to the combined effect of: (1) accelerated hydration (see Figure 1) which leads to increased consumption of water and thus increased autogenous shrinkage (Khatibmasjedi et al, 2019; Li et al, 2018); and (2) the refined pore structure of concrete caused by the presence of NaCl and CaCl 2 , leading to an increased number of small pores in the size range of 3 nm to 20 nm in the concrete (Park et al, 2011; Suryavanshi et al, 1995; Younis et al 2019). The number of such small pores was observed to increase with the salinity level (Vanhanen et al, 2008), which accounts for the increase of capillary action and drying shrinkage.…”

A review of recent advances in the science and technology of seawater-mixed concrete

“…Multiple studies have shown that seawater accelerates the early-age hydration of cement [11,[16][17][18][19][20][21][22][23][24][25][26]. Some studies show that the induction period is unaffected, while others show a shortening in the duration of the induction period.…”

“…Pore size distributions in seawater-mixed cement pastes have been studied using quantitative several techniques (mercury intrusion porosimetry, dynamic vapor sorption, specific surface area using nitrogen adsorption and Brunauer, Emmett and Teller (BET) theory) [11,17,18,[21][22][23][24]29]. Seawater reduces the porosity and causes a refinement of the pore sizes (lesser capillary pores, especially large capillary pores) [11,16,18,21,23].…”

The effects of seawater and nanosilica on the performance of blended cements and composites

“…10 Water accessible porosity and water absorption coefficient of cement mortars after 28 days of curing cases, the best performance was found for specimens SW3-P and SW3-S, showing that a combination of seawater and NS was the most beneficial in decreasing specimens' sorptivity. Many authors Etxeberria et al 2016a, b;Khatibmasjedi et al 2019) have reported that seawater contributes to decreases in the water absorption and sorptivity of cement mortars and concretes, irrespective of the type of cement used. A possible explanation for this improvement is the formation of Friedel's salt, which precipitates in the pores thus refining the microstructure and improving the permeability of the composite (Li et al 2018a;Wang et al 2018;Bertola et al 2019).…”

“…After 28 days of curing, the effects of seawater in OPC-based concrete are considered to be minor and strength improvements (if at all observable) are generally limited to 5-10%, with long-term mechanical performance being reported as slightly lower than that of OPC-based concrete produced with freshwater (Mbadike and Elinwa 2011;Etxeberria and Gonzalez-Corominas 2018;Guo et al 2018;Bertola et al 2019). Moreover, a refinement in pore structure and an improvement in the permeability of seawater-mixed composites has been reported (Ishikawa et al 2014;Khatibmasjedi et al 2019;Montanari et al 2019;Sikora et al 2019b).…”