Strength and Durability Assessment of Portland Cement Mortars Formulated from Hydrogen-Rich Water
However, no apparent relationship was found between internal water absorption and durability like impermeability, resistance to sulfate attack. Corrosion of steel reinforcement is the most serious durability problem of It impairs not only the appearance of the structure, but also its strength and safety, due to the The results of the last studies indicated a close relationship between the. PDF | Concrete must has to ensure satisfactory compressive strength and durability. The mechanical properties of concrete are highly.
High permeability led to the introduction of molecules that react and destroy its chemical stability [ 1 ]. Moreover, low permeability of concrete can improve resistance to the penetration of water, sulphate ions, chloride ions, alkali ions, and other harmful substances which caused chemical attack [ 2 ]. Concrete permeability had a close relationship with the characteristics of its pore structure in the cement paste and the intensity of microcracks at the aggregate-cement paste interface as well as within the paste itself [ 3 ].
Here, pore structure mainly involved volume and size of the interconnected capillary pores. As we know, the hydration reaction of cement results in a product consisting of solid and pore systems. The pore network of a cement paste matrix provides passage for the transport of fluid into concrete and its development depends on a number of factors including the properties and composition of the concrete constituent materials, the initial curing condition and its duration, the age at testing, and the climatic exposure during drying and conditioning of the concrete [ 45 ].
The temperature of curing and the duration of moist curing are the key factors for proper pore structure.
The effectiveness of initial curing becomes more important when mineral admixtures like fly ash are used as partial substitution for cement in concrete.
Numerous workers have reported that mineral admixtures require a relatively long curing period for the favourable pozzolanic effect on the performance of concrete to be realized [ 67 ].
Sorptivity is an index of moisture transport into unsaturated specimens, and recently it has also been recognized as an important index of concrete durability [ 8 ]. During sorptivity process, the driving force for water ingress into concrete is capillary suction within the pore spaces of concrete, and not a pressure head [ 9 ].
A detailed characterisation of the pore structure of the concrete can be analyzed by many kinds of techniques, but the advanced methods are cumbersome and are neither available nor useful for daily concrete practice [ 3 ].
Sorptivity testing is also more representative of typical field conditions. Some experts have suggested that the method can also be used to measure the total pore volume of capillary and gel pores in the concrete [ 10 ]. Martys and Ferraris have shown that the sorptivity coefficient is essential to predict the service life of concrete as a structural material and to improve its performance [ 11 ].
The water absorption by immersion is also considered to be a relevant parameter about the performance of concrete. Several experimental investigations have shown that the capillary permeability is substantially affected by the curing condition [ 12 ]. Sufficient curing is essential for a concrete to provide its potential performance [ 13 ].
Theoretical relations between sorptivity and permeability are established in the literature [ 1415 ]. However, these relations have not been extensively evaluated experimentally. In this study, the total capillary and gel pore volume was not measured directly but was estimated using the water uptake from soaking testing.
The main objective of the present work is to study the effect of water absorption on durability of concrete such as compressive strength, permeability, sulfate attack, and chloride diffusion. Within these tests, mechanical test, impermeability test, sulfate attack test, and chloride migration tests are realized. A detailed analysis is also presented in order to establish useful relationship between these parameters.
Materials and Methods 2. Materials In experimental studies, the OPC The chemical composition of this cement is given at Table 1. The crushed stone aggregates and quartz sand with a fineness modulus of 2.
The maximum particle size of aggregates is 20 mm. As a result of experiments, the specific gravities of sand and crushed stone are andrespectively. Concrete admixture used was polycarboxylate water reducers. Chemical composition of cement.
Methods All concrete mixtures were prepared in the laboratory. Cores of mm were prepared for permeability test, and mm concrete cylinders were also prepared for chloride ions diffusion testing.
All specimens were cast in steel molds and compacted using a vibrating table. In order to achieve different water absorption, specimens were subjected to different curing methods as follows: Sorptivity of concrete was evaluated by penetration height and water absorption, and the introduction of this testing method was shown in Figure 1.
For penetration height, the surface with a length of 3—5 mm of the sample was in contact with water, as shown in Figure 1. Since the surface of the sample became dark when it absorbed water, penetration height at the side of samples was observed during testing.
For water absorption, the surface and middle segments were cut from samples, respectively, and thus surface water absorption and internal water absorption were also measured.
Before testing, specimens were sealed on the top and sides and placed in a water bath so that the open bottom was constantly submerged in a depth of 3—5 mm. Weight of samples was measured after 4 days, and water absorption was measured.
A water pressure of 1. Resistance to sulfate attack was evaluated through dry-wet cycle testing. Compressive strength was measured during testing. Permeability height of concrete. Rapid migration test is a non-steady state migration using an external electrical field for accelerating chloride penetration.
The test is relatively simple and rapid with the test duration in most cases being 24 hours. The concrete samples with size of mm diameter and mm thickness were cut into 50 mm thick slices, from surface and center of samples, respectively. Results and Discussion 3. Water Absorption Permeability height can be measured through soaking testing, and results about this are given in Figure 3. It can be shown that penetration height increased apparently with time within 12 h.
For different curing methods, penetration height was not the same. It indicated that different curing conditions will cause different permeability of samples. Penetration height of samples: Sorption depends on both the capillary pressure and effective porosity.
Capillary pressure is related to the pore size through the Young-Laplace equation, and effective porosity refers to the pore space in the capillary and gel pores. In addition, different pore size leads to different capillary pressure, and capillary pressure of concrete can be calculated by the average pore size. In order to consider surface effect, both surface water absorption and internal water absorption were investigated.
Water absorption is measured by measuring the increase in mass as a percentage of dry mass. Figure 4 gives results of surface and internal water absorption. It can be seen that surface water absorption is higher than internal water absorption for all the specimens. This is due to the rapid loss of water at the cover concrete during curing.
As can be expected, higher water absorption corresponds to a higher penetration height. Under this curing condition, the surface concrete rapidly loses its water of hydration. On the other hand, for internal water absorption, samples exposed to different curing conditions presented similar results. So, curing methods has great influence on surface properties.
In order to investigate the influence of curing on microstructure of concrete, microstructure of concrete samples exposed to different curing conditions was also analyzed by SEM.
As there was a large difference in surface water absorption, microstructure of surface concrete was further studied. Figure 5 showed photos of surface concrete obtained by SEM, and Figure 5 a stands for the sample exposed to condition b, while Figure 5 b stands for the sample exposed to condition d.
From Figure 5different structures can be seen. For the sample cured in condition b, the microstructure was more compact. However, for the sample cured in condition b, there were holes and loose structure.
These are consistent with the results of water absorption. The day apparent porosity exhibited by all mortar mixtures is also shown in Figure 1. The results indicate that increasing HRW concentrations lead to lower porosity in the mortars. The day apparent porosity of HWM0.
The reduced porosity indicates the presence of fewer open pores and voids, which implies a dense microstructure. Additionally, it is presumed that in HWMs better degree of hydration leads to a reduction of capillary pore volume because capillary pores become filled with hydration products, and gel pore volume is increased as more gel is formed. This leads to reduced total porosity in the case of HWMs.
Setting time and day apparent porosity of cement mortars. Compressive, Flexural, and Splitting Tensile Strength The compressive strength development of all the mortar mixtures during the entire curing period is shown in Figure 2 a. The compressive strength results presented are the average of 6 specimens for each mortar mix. As shown in the figure, the compressive strength increased with the curing time irrespective of the mixture. The day compressive strength of all mortar mixtures was in the range of A higher strength gain for HWMs was also observed at later ages 56 and 90 days.
The percentage increase in compressive strength for HWM0. This remarkable increase in compressive strength at an early age indicates the set accelerating effect of HRW. The enhancement in compressive strength in HWMs is attributed to their more compact and dense microstructure caused by precipitation of more hydration products calcium hydroxide CH and CSH in the hydrogen-rich environment, which leads to reduced apparent porosity and fewer intermittent pores.
Those hydrated products contribute to high compressive strength by reducing the porosity and improving the microstructure of the paste matrix and interfacial transition zones in the cement-sand interface of the mortar mixtures. It is a well-established fact that the strength of cement mortars is primarily the result of a three-dimensional network of hydrate phases that offer resistance to external loads without breakdown.
The flexural strength of all mortar mixtures increased systematically with the compressive strength Figure 2 b. At all ages 7, 28, 56, and 90 daysan ascending trend was observed for flexural strength in all mixtures. The day flexural strength of all mortar mixtures was in the range of 6.
The highest day flexural strength was in HWM0. The variation in the splitting tensile strength of the mortar specimens with age is shown in Figure 3. The splitting tensile strength did not show a significant increase in mortars fabricated using low concentrations of HRW 0.
The highest splitting tensile strength of 2. Unlike the compression and flexural strength results, relatively fewer sharp variations in tensile strength were observed. In general, HRW has a positive effect on the splitting tensile strength of mortars, which we attribute to its filling effect caused by the precipitation of more cement hydrates.
Variation in the splitting tensile strength of mortar mixtures with age.
Evaluation of Relationship between Water Absorption and Durability of Concrete Materials
The HRW increases the pH of normal water from 7 to It is stated elsewhere [ 27 ] that, at a pH value below 8. However, at an increased pH value, calcium and silicate species exist as hydroxylated species Ca OH 2 and silicate anions, respectively.
Aluminum, silicate, and iron are also present in lower amounts [ 29 ]. Capillary Absorption The absorption and transmission of water, capillary absorption, indicate the volume of voids in cement mortar systems. A higher capillary absorption value indicates more permeable voids. Water is the carrier of various harmful ions; therefore, capillary absorption is an important test for the durability of construction materials. Generally, higher mechanical strength correlates with a lower capillary absorption coefficient.
Figure 4 shows the capillary absorption coefficient for all the mortar mixtures at 28 days. In this figure, it is observed that increase in HRW concentration results in the reduction in capillary absorption. The higher uptake of water in CWM0 is caused by its larger capillary pores, whereas the lower water uptake in the HWMs occurs because they have fewer interconnected flow channels.
In the HWMs, the hydration products occupy more space than they do in CWM0; in other words, the formation of hydration products reduces capillary porosity.
Thus, the higher degree of hydration leads to decreased capillary porosity [ 30 ]. Capillary absorption coefficients of mortar mixtures at the curing age of 28 days. As shown in the figure, the UPV values increase with curing age irrespective of the mixture. Factors such as pore structure, material properties, mix proportion, and the interfacial zone between aggregates and cement paste all affect UPV values.
It is ascertained that HRW induces precipitation of more hydration products compared to the CWM, leading to denser, more compact microstructures.
As a result, the porosity of the cement matrix was reduced and the continuity of pores diminished. As expected, the use of HRW increased the density of mortar because the higher degree of hydration leads to the formation of more cement hydrates and reduced apparent porosity.
- Evaluation of Relationship between Water Absorption and Durability of Concrete Materials
- Strength and Durability Assessment of Portland Cement Mortars Formulated from Hydrogen-Rich Water
A significant increase in ER was noticed with age for all mixtures. As shown in the figure, the ER exhibited by all mortar mixtures at the curing age of 28 days was found to be in the range of 7— According to ACI [ 32 ], corrosion is less likely to occur when ER is equal to or greater than At 28 days, that criterion was met by only HWM0.
Moreover, it is ascertained that the increase in HRW concentration enabled mortars to develop a denser, more compact microstructure, which reduced the interconnectivity between pores and thus resulted in higher ER.
That is, it is presumed that the denser microstructure, less-continuous pore system, and reduced porosity allow the HWMs to demonstrate better resistivity. ER is an important parameter that governs the corrosion of reinforcement in concrete. The densification of microstructures increases both ER and the compressive strength of mortars [ 33 ]. It is known that as the compressive strength increases, the ER also increases. Some researchers have found a significant correlation between the two parameters, which led them to formulate logarithmic, exponential, and linear relationships [ 34 ].
In this investigation, we observed an exponential relationship between compressive strength and ER at all curing ages, with a regression coefficient of 0.
It is presumed that alkaline environment in the pore solution HWMs would provide an appropriate environment for the steel bars embedded so that they can passivate and remain passivated against corrosion. The increased alkalinity leads to a denser pore structure, which apparently is overweighing the increased ionic concentration in pore water. The kinetics of the hydration process can be studied by measuring the amount of unreacted C3S alite in the XRD pattern as a function of hydration time [ 38 ].
Additionally, due to lesser crystalline nature of calcium silicate hydrate, it is difficult to identify it.
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Therefore, the amount of calcium hydroxide portlandite content in the hydrated cement paste would be an indication of the formation of the hydrated product. According to Neville [ 40 ] the progress of cement hydration can be determined predicting the calcium hydroxide content. The degree of hydration is a fundamental parameter for cementitious materials because the evolution of mechanical properties greatly depends on it [ 42 ].
Microstructure Investigations Our study of the microstructure of the mortars presents an internal structure that includes CH, CSH, and micropores. The mechanical and durability performances of mortars are greatly influenced by their microstructures, which can be shown in SEM micrographs.
It is evident that the HWM0. According to Ramachandran et al. Regarding durability, it was deduced that the microstructures of mixtures with HRW get denser and more packed, especially at advanced ages. Concrete durability greatly depends on the microstructure and product uniformity of the cement paste; thus the growth and development of CSH are a decisive factor for concrete performance in terms of durability [ 44 ].
Moreover, Ca OH 2 also plays a vital role in concrete durability; it is the source of high pH in the concrete pore fluid, which holds relevance in terms of chemical attacks such as corrosion and alkali silica reaction [ 30 ]. The evolution of strength, durability related, and time-dependent properties of concrete materials are highly dependent upon microstructure of cement paste.
Thus, promoting the more homogenous growth of cement hydrates positively affects the durability of concrete, as observed in our HWMs.
Conclusions To evaluate the effects of HRW on the mechanical performance and durability of cement mortar systems, we carried out an experimental investigation. The experimental study led to the following conclusions: The effect is greatly pronounced at an HRW concentration of 0. The fast setting time is an indication of accelerated hydration. Use of HRW reduced the apparent porosity of mortars, indicating the formation of the dense microstructure.