The aim of this work is to better understand the physical and chemical phenomena involved in hydrated mix (clinker + addition) during the natural carbonation process, to characterize cement with supplementary cementitious materials (SCMs) under various curing environment. The prepared cement pastes were characterized by thermogravimetric analysis. The results showed a considerable influence of the environment on the properties of mortars and cement and a perfect correlation between compressive strength, natural carbonation, nonevaporable water, and portlandite content. It was observed that the reduction of the curing period makes the mortars more sensitive. The kinetics of process was evaluated from Ca(OH)2 content and nonevaporable water contained in mortars. These two parameters reflect the hydration progress of the water/cement ratio studied. The weight loss due to Ca(OH)2 decomposition, calculated by DTA/TG analysis, shows the effect of the pozzolanic reaction and the natural carbonation. The supplementary cementitious materials (SCMs) play a considerable role in the slowing down of the aggression environment.
Obviously, there is a close link between CO2 concentrations in atmosphere and materials, especially the cementitious materials, making them able to be carbonated. The carbonation depth is evidently higher with a great level of CO2. The carbonation rate depends on the infiltration of carbon dioxide into the cement matrix. The interior humidity and environment exposure of cement matrix determine saturation level and CO2 transfer. So the presence of humidity source is primordial [
The carbonation effect consists in the action of atmosphere especially CO2 gas. It is diffused into concrete voids and dissolves to acid. This medium changes lead to the dissolution of hydrates especially the portlandite. The carbonation effect rate depends on many parameters; we mainly focused on two of them, the porosity and the portlandite content. Indeed, the portlandite content is a key parameter if we are interested in the carbonation and its buffering effect on the interstitial pH solution through a hydroxide ion on dissolution release. This solution is also accompanied by a release of calcium ions Ca+2, which are able to react with the carbonate ions
The supplementary cementitious materials (SCM) in blended cement have a pozzolanic or hydraulic characters; they can modify the cement hydration and also contribute with cementitious products to the matrix structure [
The ordinary Portland cement (OPC) is more resistant to carbonation than blended cement with pozzolanic additions, if the different buffering effects of their hydrated phases and alkali contents are considered. In the absence of carbonation or any other attack [
Several studies [
Portlandite content of cementitious materials is a durability and performance indicator of concrete structures against carbonation because the portlandite represents the basicity reserve of cementitious materials; it maintains a high pH of 12.6 [
The main objective of studies is the determination of the carbonation front to prevent corrosion of steel in reinforced concrete. The kinetics of carbonation is influenced by the amount of corrosion products [
When clinker is substituted by some SCMs, portlandite content decreases and concrete became sensitive to carbon dioxide presence. The mechanical strength is closely related to the portlandite content. In carbon dioxide diffusion process, relative humidity plays an important role because the diffusion coefficient of carbon dioxide in the air is ten thousand times higher than in water [
A higher pH level (12.4) protects steel from corrosion. In front of the great diversity of hydraulic SCMs used today, the data like mechanical strength, W/C ratio, or cement content are insufficient to translate complexity of the cementitious materials. For example, some SCMs, such as the mineral additions, consume a party of portlandite through chemical reactions as the case of pozzolanic reactions. For these additions, they reduce porosity of cementitious materials and a good mechanical strength is reached, on account of high particles fineness which plays the role of fillers to fill the voids like silica fume. Thus, from chemical point of view these new materials may be durable due to a low portlandite content; from physical point of view they constitute an effective obstacle to CO2 penetration.
A compromise could be found to properly formulate these cementitious materials and ensure their durability. Calculating the portlandite content as a chemical indicator, porosity, and permeability like physical indicators allows solving this kind of problematic situation [
The necessity for curing time and conditions occurs from the fact that cement hydration takes place only in water filled capillaries. So, in order to obtain a good mortar or concrete, the setup of an appropriate mix must be followed by the curing in appropriate environment during the early ages of hardening and water loss capillaries by evaporation must be prevented [
Taking into consideration the action of carbon dioxide, the curing period is a determining factor in the behavior of cement. If the conditions and curing time are sufficient, slag and pozzolanic cement have a good carbonation resistance [
It is necessary that the relative humidity of the storage medium is greater than 80%, so that the cement hydration process continues. The convenient curing of concrete facilitates the cement hydration which leads to improve mechanical properties of concrete. Extended wet cure period of concrete causes a decrease of carbonation concrete depth [
However, the curing period should be extended to 14 days when the cement contains SCMs, such as slag and fly ash, due to the slow hydration reactions between them and the calcium hydroxide. This reaction requires the presence of water to produce the cement hydrates and contributes to filling the capillary voids.
Sajedi and Razak shows that the effect of the first week of underwater cure of OPC 50 mm mortar cubes after mixing is equal to or even more than 12 weeks of underwater cure after the first week of mixing [
Aitcin et al. recorded the difference of compression strength at the order of 17% to 22% between concrete samples that are stored in air and wet [
For a given cement content, carbonation is more important for a concrete CEM II/B (20% of limestone fillers) than for a CEM I concrete. For a cement content of 250 Kg/m3, the carbonation depth for CEM II/B-based concrete is about 30% higher than CEM I-based concrete, whatever the curing time. Therefore, the carbonation depth is related to clinker dosage [
In this study, we are interested specifically to the relation between wet cure and mechanical and chemical properties of mortars and cement. Four types of cement were prepared (clinker effect is taken into account in the preparation of cement with the various SCMs), plus artificial Portland cement (CEMI) as a reference. The TG analysis quantifies the carbon dioxide fixed to each type of hydrate (CSH) in different medium and at different time. Nonevaporable water was used to determine the hydration degree of cement.
Four cement types from the same clinker were prepared; we have characterized as completely as possible a compound cement (CPL30%-CEMII/B-S) class 32.5 MPa with 30% of slag and a (CPZ30%-CEMII/B-P) class 32.5 MPa with 30% of pozzolana, to be compared to (PC-CEMI) 52,5 MPa (Portland cement PC) and a (CRS-CEMII) class 42.5 MPa with secondary additions (cement sulphate resistant); this is to better locate the slag cement and pozzolanic blended cement.
Algerian local products (clinker, gypsum, slag, and pozzolana) were crushed to a particle size less than 1 mm before being thoroughly mixed. Because of the hardness, strength, and abrasion of the clinker the separate grinding of raw materials was adopted, which consequently improves the physical and thermal characteristics of modified cement and enhance the properties of these materials [
The dosage of natural gypsum was kept constant at 5% for two reasons, first to regulate setting time and secondly to not hide the effect of addition on the mechanical properties of cement. These were divided and prepared to the proportions given in Table
Composition of the different mixtures [
Mixtures | Clinker [%] | Gypsum [%] | Slag [%] | Pozzolana [%] | Additions secondary [%] | Design mixtures | NF EN197-1 |
---|---|---|---|---|---|---|---|
CP |
95 | 0 | 0 | 0 | 0 | Control cement | CEMI52.5 |
CR |
88 | 5 | 0 | 0 |
7 | Binary cement | CEMII42.5 |
CL30 |
65 | 5 | 30 | 0 | 0 | Binary cement | CEMII/B-S32.5 |
CZ30 |
65 | 5 | 0 | 30 | 0 | Binary cement | CEMII/B-P32.5 |
Blended cement (cement based added) = addition/clinker (%).
CP
CR
CL30
CZ30
Chemical composition of cement used (%) [
Cement | CaO | SiO2 | Al2O | Fe2O3 | MgO | TiO2 | Na2O | K2O | P2O5 | SO3 | L.O.L |
---|---|---|---|---|---|---|---|---|---|---|---|
CEM I | 64.24 | 20.25 | 5.13 | 3.73 | 1.69 | 0.26 | 0.16 | 0.62 | 0.11 | 2.28 | 1.53 |
CEMII | 63.29 | 21.18 | 4.37 | 4.77 | 1.46 | 0.19 | 0.12 | 0.29 | 0.17 | 1.14 | 3.02 |
CEMII/B-S | 44.4 | 36.1 | 4.73 | 4.57 | 2.3 | 0.29 | 0.49 | 0.16 | 1.98 | 2.19 | 3.06 |
CEMII/B-P | 43.66 | 35.25 | 8.42 | 3.67 | 1.5 | 0.34 | 1.01 | 1.65 | 0.13 | 2.41 | 1.96 |
Mineralogical composition (%) and physical characteristics [
Cement type | Blaine specific |
Specific density |
C3S | C2S | C3A | C4AF |
---|---|---|---|---|---|---|
CEM I | 3420 | 3.15 | 59 | 13 | 07 | 11 |
CEMII | 3210 | 3.18 | 54 | 20 | 04 | 15 |
CEMII/B-P | 3750 | 3.1 | 57 | 17 | 07 | 11 |
CEMII/B-S | 3210 | 3.12 | 59 | 17 | 07 | 11 |
The standard sand CEN (ISO standard sand) is clean natural siliceous sand including its fine fractions with the grains generally rounded and isometric. It was dried, screened, and prepared in a modern workshop with a required quality and coherence according to the certified standard CEN EN 196-1, ISO Standard Sand, and ISO 679: 2009 [
The water is drinking quality water in regard to the requirements of standard NF P 18-404.
All normalized mortars were prepared by mixing 1350 g of normalized sand, 450 g of cement, and 225 g of water. These samples were demolded after 24 h and placed in water bath maintained at 23°C. Compressive tests were carried out on mortars at different ages according to EN 196-1 [
Reference samples were kept in air-conditioned room (RH = 65%,
To assess compressive strength six samples were tested. Size of samples for pure paste was cylindrical (2.5/5.5 cm) and prepared and conserved in such conditions in humid room (
The tests were performed according to standard NF EN 196-1. The half-prisms were taken to a compressive machine to assess the compressive strength. The resistance is calculated using the formula: compressive strength = load (
Natural carbonation in air-conditioned room (
The thermal gravimetric (TG) analysis measures the difference of masses between a reference and specimen sample. The differential thermal analysis (DTA) records the difference of temperature with thermocouple located under the nacelles. These two analyses have been recorded using Netzsch STA 409 machine. Tests were carried out from 20°C up to 800°C under reconstituted air (80% N2 and 20% O2) with a constant heating rate (10°C/min) in alumina crucible.
Figure
Effect of wet curing time on the mechanical performance.
These curves shows that, on the one hand, the compound cement has a different kinetics of CPA (CEMI) and the CRS (CEMII) and slow kinetics in the long term and the resistance class for composite cement is much lower than those of the CPAs and CRS. This is explained by the low content of clinker in cement which considerably lowers down their hydration especially at young age. This is in agreement with the results of previous research works [
The specimens left exposed to air presented the lowest resistance. However, those undergoing a curing regime gave the best results. An approximate explanation is that in the test pieces having been left untreated for one year a large part of their mixing water is evaporated. As a result, the hydration of the cement and the development of resistance have been stopped. Moreover, conservation in the laboratory conditions favors the development of microcracks inside the test pieces, which resulted in the decrease of the resistances after one year of age.
At one year the difference between the resistances of the treated and untreated specimens increased considerably. Indeed, for a CPA mortar, an increase in the cure duration of 3 days relative to the control mortar increases the strength of 2%, 6.4% (7 days of treatment/control), and 14% (28 days of treatment/control). For a CRS mortar a longer curing time of 3 days compared to the control mortar increases the mechanical strength by 5.6% which is 17.61% (7 days of cure/control) and 23% (28 days of cure/control), respectively. For the mortar CZ30% the three-day cure time duration relative to the control mortar increases the mechanical strength by about 8.2%, 39% (7 days of cure/control), and 48% (28 days of cure/control), respectively. For the mortar CL30% the three-day cure time with respect to the control mortar increases mechanical strength of 23.05%, 48.1% (7 days of treatment/control), and 64.15% (28 days of treatment/control), respectively.
Indeed, underwater maturation promotes hydration, especially to the skin of surface of the samples, which progressively increases their compactness because hydration consumes the internal water causing the reduction of its content and the solidification of the concrete. The underwater cure promotes the formation of the hydrates leading to the filling of the pores by means of a continuous supply of water, leading to the improvement of the porosity. While in the case of the “air” conservation control, the upper part is rapidly dried, which slows down the hydration and leads to low compressive strengths [
A good continuous cure at a relative humidity is still favorable to a better hydration in cement [
The most widely used technique for quantifying the carbonation kinetics is the detection of a limit below which the pH is around 9, which is called the carbonation front detected by the colored turn of the phenolphthalein. The latter is spread on a freshly split sample; the noncarbonated part is colored pink while the carbonated part remains colorless.
Natural carbonation was in an air-conditioned room (
Figure
Continuous air cure for one year.
During air conservation of samples, the superficial part dries quickly, which slows the hydration and leads to a greater depth of carbonation. CL30% mortar affected by a high carbonation depth, insufficient wet cure, clinker substitution by slag, and the amount of Ca(OH)2 will be reduced in part by the low amount of Portland cement and on the other hand by the pozzolanic reaction (consumption of the portlandite). Therefore, the introduction of the natural additions in mortars leads to a low portlandite Ca(OH)2 content. As a result, a smaller amount of CO2 is needed to react with calcium to consume the whole of portlandite, so that the pH falls more easily [
Figure
Influence of wet curing regime on the carbonation attitude of cement at one year.
The duration of wet curing significantly decreases the carbonate depth, especially when the clinker dosage is lower.
The dosage of the clinker decreases and makes higher kinetics of carbonation. This is directly attributed to the role played by the porosity of cementitious matrix. Indeed, the more the clinker of lower dosage, the more the porosity, leaving voids that favor, on the one hand, the movement of the free water located more deeply in the mortar and on the other hand the penetration and the diffusion of the carbon dioxide [
In fact, for an increase in the curing time of 3 days, it is possible to decrease the carbonate depth by nearly 20% for a CPA cement by comparing the control to the air at one year with a registered decrease of 43% and 57% for 7 days of cure/control in air and 28 days of cure/control in the air, respectively.
For CRS cement, we registered a reduction rate of 33% at 3 days, 44% at 7 days, and 55% at 28 days of cure against control specimen in a simple air curing. For CZ30%, we noted 33% of reduction at 3 days, 42% at 7 days, and 50% at 28 days. The mortar with CL30% cement marked 21% of reduction at 3 days, 29% at 7 days, and 43% at 28 days.
This reduction is caused by lime content of clinker. More lime in cement induced lower carbonation. Slug and pozzolan cement contain less of portlandite than CPA and CRS ones.
The formation of calcite during CPA cement carbonation results in the formation of a protective layer on the skin of material which slows down the diffusion of carbon dioxide, so carbonation can be stopped. In the addition-based cement, and in the absence of the quantity of portlandite sufficient to form the protective layer, carbon dioxide diffuses more rapidly [
Figures The peak 50 to 150°C: in this section we observe the removal of the adsorbed and free water. We see also the decomposition of CSH part [ The peak 105 to 450°C: this is the range of decomposition of CSH and ettringite [ The peak 450 to 550°C: this is the decomposition of CH [ The peak 650 to 750°C: this is due to the decarbonation of calcite CaCO3 [
From Figures
DTG/TG cement paste preserved on air (RH = 65%,
DTG/TG cement paste preserved in wet cure (RH = 95%,
The same behavior for Figures
DTG/TG cement paste preserved on air (RH = 65%,
DTG/TG cement paste preserved in wet cure (RH = 95%,
The decomposition of the portlandite at 28 days is found that, in the 2nd endothermic peak in the DTA curves between 450°C and 550°C, the loss of mass in this range represents the lost water due to the dehydration of Ca(OH)2.
The total CaCO3 content was calculated from the weight loss recorded in the ATG curve between 600°C and 800°C, whose intensity increases with the addition contents as a function of the preservation medium; the loss of weight caused by the CO2 effect is due to the decarbonation of CaCO3.
According to the curves, the calcium hydroxide Ca(OH)2 content of calcium hydroxide for cement stored in the wet conditions is higher than that of air and the CaCO3 content of the cement preserved in the air is more important due to the natural carbonation, highlighting the 65% drying effect especially on cement with a high additive contents, minus the quantity of portandite produced.
Figures
(a), (b) Thermogravimetric analysis of cement paste preserved in wet cure and stored in the air for 2 days.
Wet cure
Air
The weight loss decreases with the substitution rate rising of the addition and under the effect of the curing medium over all the temperature ranges. When the temperature range is between 105°C and 450°C an important loss of weight is noticed and due to the evaporation of water (H2O) chemically bonded to CSH hydrates for cement at the age of 2 days in a humid room. They are 3.11%, 2.76%, 2.08%, and 1.72% for the samples of artificial Portland cement CPA, CRS, CL30%, and CZ30%, respectively. For air-cured cement at the age of 2 days they are 2.29% 2.13%, 1.42%, and 1.4% for CPA artificial Portland cement, CRS, CL30%, and CZ30% samples, respectively.
The weight loss decreases proportionally with the substitution rate of the addition as for the curing medium influence. Replacing a part of cement with mineral additives made the hydration reaction be slower and could result in several effects: Dilution of the clinker part of the cement with concomitant reduction of the calcium aluminates and silicates content of the cement and consumption of the lime resulting from the hydration of the clinker (the pozzolanic reaction) which occurs at a young age. Reduction of portlandite content, a compound vulnerable to external attacks [ A reduced amount of hydrated cement consequently decreasing the compressive strength with a greater carbonation depth especially, for cement with a higher addition content preserved in air causing a negative effect on the chemically bound water contained in the CSH hydrates [
Figures
(a), (b) Thermogravimetric analysis of cement paste preserved in wet cure and stored in the air for 28 days.
Wet cure
Air
The results obtained from the loss of weight due to the evaporation of the water chemically bound to the hydrates CSH for cement preserved in the humid chamber is 7.5% for the CPA and 5.04%, 4.6%, and 3.07% for the CRS, CL30%, and CZ30%, respectively. Thus, for air-cured cement it is about 6.9% for CPA artificial Portland cement and 3.2%, 2.2%, and 2.77% for samples of CRS, CL30%, and CZ30%, respectively.
A clear increase is observed by comparing these values with the results obtained during the cure of 2 days due to the progress of the hydration process.
The evolution of weight loss due to the evaporation of water of the cement preserved in the wet conditions is greater than air, the same observation for portandite content; this is attributed to the hydration reaction process. At 65% of relative humidity, the portlandite formation is almost stopped for all cement. This can be interpreted by the tendency towards the end of hydration process in this mode of conservation.
Figures
(a), (b) The content of retained portlandite in cement paste in wet cure and left in the air for 2 days.
Wet cure
Air
The tests were carried out on cement pastes corresponding to the different compositions. The objective is, on the one hand, the monitoring of the quantity of portlandite and, on the other, the study of the effect of the quantity of portlandite as one of the indicators of durability on the kinetics of natural carbonation.
The method of assaying portlandite and calcium carbonates by TGA is based on the molar masses (atomic); the objective was the control of portlandite quantity and the study of its effect as one of durability indicators on the natural carbonation kinetics.
The decomposition of portlandite generally occurs in the temperature range of 450°C to 550°C; its decarbonation takes place in the temperature range of 600 to 800°C [
From portlandite’s dosage of cement pastes, the profile of the portlandite Ca(OH)2 content of the carbonation mechanism is analyzed.
The portlandite quantity from cement pastes was derived from TGA tests carried out on mass reduced samples shown in Figures
At 2 days of hydration for a wet cure (cement control) CPA, the portlandite content decreases from 3.55% to 1.68% compared to air curing with values from 2.14% to 2%, 1.82% to 1.42%, and 0.72% to 0.41% for the samples of CRS, CL30%, and CZ30%, respectively. The same was also observed for 28 days of hydration for a wet cure (cement control) CPA; the content of portlandite decreases from 10% to 6.57% compared to air curing from 3.22% to 3.1%, 2.3% to 1.86%, and 1.27% to 0.95% for CRS, CL30%, and CZ30% samples, respectively. After 28 days, this can be explained by the decrease in the amount of portlandite as the quantity of portlandite formed is all the more important as the content of mineral additions is lower. This result is in agreement with other research works [
As the pozzolanic effect becomes hydrated, the cement releases portlandite ions (Ca++ and OH−) and then, progressively, the pozzolana and/or the slag captures the Ca++ ion to form CSH or aluminates. The hydration reaction between Portland cement and a cementitious addition is slower. The slowdown phase has become a dormant phase [
Figure
The content of portlandite as a function of curing medium for all cement.
The dehydration of calcium silicate hydrates (CSH) generally occurs in the temperature range of 105 to 450°C. The amount of CSH which reflects the progress of the hydration reaction is estimated by the quantification of the loss of weight due to the evaporation of the water bound to these hydrates; the amount of nonevaporable water was calculated by the following relationship [
The nonevaporable water of the cement as a function of age and the curing medium is represented in Figures
(a), (b) Nonevaporable water of cement pastes retained in the wet cure and air at 2 days.
Wet cure
Air
Depending on the type of cement, at 2 days of hydration for a wet cure (cement control) CPA, the amount of nonevaporable water (NEW) decreases from 3.11% to 2.29% compared to air and 2.76% to 2.13, 2.08% to 1.42%, and 1.72% to 1.4% for the samples of CRS, CL30%, and CZ30%, respectively. The same was also observed for 28 days of hydration for a wet cure of CPA (control cement). The amount of nonevaporable water decreases from 7.5% to 6.9% when compared to air and 5.04% to 3.2%, 4.6% to 2.2%, and 3.07% to 2.77%, respectively, for samples of CRS, CL30%, and CZ30%, respectively.
The amount of nonevaporable water (NEW) in the control cement is higher than the compound cement; this is attributed to the degree of polymerization of the CSH gel and also to the pozzolanic CH-depletion of the composite cement. As the hydration phenomenon is delayed by the presence of secondary additions.
Figure
Nonevaporable water in relation to curing medium for types of cement.
As can be seen from Figure
Portlandite content as a function of carbonation depth.
Wet cure
Air
The trend curves in the Figure
Portlandite content as a function of compressive strength.
Wet cure
Air
As a function of the general tendency for the two curing media, Figure
Carbonation depth as a function of compressive strength.
Wet cure
Air
For the mechanical strength as a function of carbonation, the proposed correlation coefficients give a good correlation for the two media (
A good correlation exists between the two quantities (Figure
Portlandite content as a function of nonevaporable water.
Wet cure
Air
Nonevaporable water is estimated by quantifying the loss of weight due to the evaporation of chemically bound water in the range of 150–450°C due to the decalcification of portlandite. This content for the samples conserved in the humid room is greater than that for air conservation, which reflects the amount of CSH due to the progress of the hydration reaction, the same findings for the content of the portandite; this is attributed to the progress of the hydration reaction. On the other, hand drying at 65% relative humidity almost stopped the formation of portlandite for all the compositions studied.
The amount of nonevaporable water (NEW) in the control cement is higher than the compound cement; this is attributed to the degree of polymerization of the CSH gel and also to the pozzolanic CH-depletion of the composite cement. Thus, the hydration phenomenon is delayed by the presence of secondary additions.
The curves represented in Figure
Nonevaporable water as a function of compressive strength.
Wet cure
Air
This work aims to quantify the effects of wet cure duration on the different chemical and mechanical properties of one-year-old mortars and cement pastes mainly and the durability regarding natural carbonation and compressive strength as studied characteristics. The investigation by thermogravimetric analysis on the cement paste allowed us to build a more clear idea at the level of the microstructure and to highlight the good correlation between the parameters seen by this analysis and the properties of mortars studied. The characteristics studied are strongly related to the wet curing regime and the influence of cement type. The results obtained from this research allow us to draw the following conclusions: The curing regime period and clinker have a significant effect and improvement of mortars properties. It has been noticed that the extension of the curing regime has a marked effect on the compressive strength. The influence of cement type is more significant for mortars with low addition dosages; the compressive strength of CEMII/BS and CEMII/BP cement is much lower than those of CEMI52.5 and CEMII42.5; this was explained by the slowing down of hydration because of the low clinker content. The carbonation depth is greater for the CEMII/BS and CEMII/BP test specimens compared to CEMI52.5 and CEMII42.5; this effect is in part attributed to the low clinker content and therefore the content of portlandite Ca(OH)2 and the pozzolanic activity. The thermogravimetric analysis (TGA) is the most optimized method for investigating natural carbonation in mortars and cement pastes. The analysis by DTA/TG shows the influence of the type of cement on the loss of weight and the content of portlandite. The quantity of portlandite is inversely proportional to the increase in the substitution rate of the addition for all ages. The cement hydration is delayed by the pozzolanic activity of the addition, which is explained by the greater carbonation depth and a lower portlandite content. A good correlation exists between compressive strength and natural carbonation. An almost linear relationship has been observed between different mortars and resistance increases when carbonation decreases. Portlandite content is increasing as a function of the compressive strength and the inversely is decreasing in regard to the natural carbonation. The nonevaporable water contained in the hydrates which reflects the rate of advance of the hydration is used to determine the degree of hydration of the blended cement. The quantity of nonevaporable water is inversely proportional to the increase in the substitution rate of the addition for all ages. The correlation between portlandite content, compressive strength, and natural carbonation was satisfactorily performed; the portlandite content seemed to be an important parameter in the prediction of the resistance of mortars and their durability.
The corresponding author Miss Saida Boualleg declares that there are no conflicts of interest for the author and coauthors regarding the present submitted article.