Evaluation the effect of lime on the plastic and hardened properties of cement mortar and quantified using Vipulanandan model

Abstract In this study, the effect of lime content (L %) on the plastic properties such as water-cement ratio (w/c), setting times, flowability, compressive, flexural and bond strengths of cement mortar were investigated. Based on the information in the literature the amount of lime varied between 0 to 45% (by weight of cement). The experimental results were compared with the data collected from different research studies and quantified using two different models. The plastic and hardened properties of the cement mortar modified with different percentage of lime were conducted according to the ASTM and BS standards. Based on the literature data the water to cement ratio (w/c) ranged between 0.3-0.74 percent, the w/c of 0.5 was selected in this study. The compressive and flexural strengths of cement mortar modified with lime up to 28 days of curing were ranged between 3 MPa to 65 MPa and 2 MPa to 12 MPa respectively. The compressive, flexural and bond strengths of the cement mortar decreased with increasing lime content. Vipulanandan correlation model was used to correlate the relationship between lime with consistency, setting times, flowability and compressive strength of cement mortar. Compressive and flexural strengths of cement mortar modified with lime were quantified very well as a function of w/c, lime content and curing time using nonlinear relationship.


Introduction
The mortar is a composite material consisting of a mixture of cementitious material (cement), ne aggregates (sand), an amount of water required for hydration reactions. Mineral admixtures, such as y ash, lime, and silica fume have been widely used for the manufacture of cement mortar. The addition of mineral additive improved the performance, mechanical properties and durability of cement mortar also, the addition of mineral additives decrease CO emission and may also reduce the adverse environmental e ect caused by cement production [1][2][3][4][5][6][7][8].
The Limestone is calcareous sedimentary rock mainly consisting of calcium carbonate (CaCO ), commonly called calcite. Limestone is used in cement and mortar for various purposes, as a raw material for clinker production and as coarse or ne aggregate. Lime is produced by nely grinding limestone in quarrying operations and has been suggested for use as an additive in Ordinary Portland Cement. Replacing of limestone into Ordinary Portland Cement has been studied [4,9,10]. Lime has been considering as an inert ller material that improves the hydration rate of cement compounds and consequently increases the strength at early ages. The incorporation of limestone powder with Portland cement has many advantages on initial compressive strength, durability, and workability. Workability, strength, and durability are three basics properties of cement mortar [11][12][13][14][15][16]. The increase in w/c reduced the value of mechanical properties and increased the workability. Several research studies have been performed to understand the e ect of lime on the physical and mechanical properties of cement mortar (Table 1). Compressive and bonding strengths are the most critical property of cement mortar that describes its quality and performance for construction works. In addition, most of the other features such as exural strength was improved in parallel with the increase in the compressive strength. In terms of compressive strength, the addition of hydrated lime to cement based mortars shows that lime-rich mortars are able to withstand a higher degree of deformation before fail-ure. The observations made, indicate that the lime additions allow for some accommodation of movement either under compressive loads or shear loading, and unlike the brittle failure of cement rich mortars, those with high lime content (where volume of lime is twice that of cement, e.g. 1:2:9 mortar) some elastic-plastic deformation is observed prior to brittle failure with increased lime content.
Although a reduction in compressive strength may be viewed as a negative result of hydrated lime addition to a mortar, the resulting performance does provide some accommodation from minor movement of the masonry, thus reducing the associated cracking, as typically seen with high strength (cement rich) mortars which although strong are more "brittle" [17][18][19][20][21][22][23][24].
In this study, the e ect of lime on the workability, setting times and mechanical strength of cement mortar were performed based on experimental and collected data from the literature. The in uence of water to cement ratio, curing time and lime content on the compressive, exural strengths of cement mortar were quanti ed using a nonlinear model.

. Objectives
The primary objective of this study is to investigate and quantify the e ect of lime on the properties of plastic and hardened properties of cement mortar using experimental and collected data from the literature. The speci c objectives are as follows: 1. Statistical variations of the compressive and exural strengths, water to cement ratio and lime content of cement mortar. 2. Investigate the e ect of lime on the consistency, setting times, owability and strength properties of cement mortar. 3. Develop a non-linear relationship to predict the compressive and exural strengths of cement mortar as a function of w/c, lime content and curing time using the experimental data and data collected from the literature. 4. Develop the relationship between compressive and exural strengths of the cement mortar modi ed with lime up to 28 days of curing. 5. To evaluate the relationship between the tensile bonding strength of cement mortar with lime content at seven days of curing.

Materials and methods . Materials
The type of cement used in this study was Gasin Portland Cement from the Gasin Cement Company (Iraq, Kurdistan-Region, Sulaymaniyah City, and 35 • 33 26 N 45 • 26 08 E). Lime is typically used in the form of quicklime (CaO) or hydrated lime (Ca (OH) ). Quicklime (CaO) is manufactured by chemical processes that transform calcium carbonate (limestone -CaCO ) into calcium oxide (CaO). When quicklime reacts with water, it turns into hydrated lime.
Tap water was used in this study.
The sand used in the study was CEN standard sand which is well graded rounded particles having a silica content of 98 % as speci ed in EN 196-1 standard requirements [8,25].

. Methodology
The plastic and hardened properties of cement mortar modi ed with lime were tested according to ASTM and BS standard. At least three samples were tested for each condition.
X-ray di raction (XRD) analyses were performed to determine the chemical composition of cement and lime at 25 • C. The powder ((2 g) was placed in an acrylic sample holder (3 mm) depth. The samples were analyzed by using parallel beam optics with CuKα radiation at 40 kV and 30 mA. The samples were scanned for re ections (2() from 0 • to 90 • in steps of 0.02 • and a 2 sec count time per step. A similar procedure was conducted by [26]. The chemical composition of the cement and lime are illustrated in Table 2 and Table 3.

Standard consistency test (BS EN 196-3:2016)
This test aims to determine the minimum quantity of mixing water to initiate a chemical reaction between water and cement. Cement is one of the materials which the right amount of water leads to attaining required cement strength. The standard consistency was carried out according to the EN 196-3 standard using the Vicat apparatus. The cement paste was prepared by putting 500 g of cement into the bowl of the mixer. The amount of water was added to the cement. Firstly, the mixing was left for 10 seconds for absorption. Then the mixing apparatus was put at a low   speed for 90 seconds then stooped the mixture for 30 seconds to bring the cement that located beyond the mixing zone. After that, the mixer restarted at a low rate for 90 seconds [13]. Without excessive compaction or vibration, the paste was quickly put into the mold which is placed on a glass plate and placed on the plate of the Vicat apparatus. The cement consistency which will allow the Vicat plunger to penetrate to 6 ± 2 mm point from the bottom of Vicat mold is known as standard consistency. The same procedure was repeated when the lime was added to the cement ( Fig. 1).

Setting time test (BS EN 196-3:2016)
The setting times were determined by observing the penetration of a needle into a standard consistency cement paste until it reaches a speci ed value. It is necessary to evaluate the setting times of the hydraulic binders to regulate the time available for the in situ application of mortars. Setting times were measured using the Vicat [27,28]. Generally, Initial setting is the time elapsed between the moment water is added to the cement to the time at which paste starts losing its plasticity. The nal setting time of cement is the time elapsed between the moment the water was added to the cement to the time at which paste has wholly lost its plasticity and attained su cient rmness to resist certain de nite pressure (Fig. 1).

Cement mortar preparation (BS EN 196-1:2016)
After mixing the materials, the mortar lled cubic molds with a dimension of (4 x 4 x 16) cm. The mortar put into the mold in two layers and by applying to the mold 60 shocks each time using the shock device. After that, the mold was leveled and covered with a plastic bag and stored in the room temperature. After 24 h from the of the mixing procedure, the specimens removed from the mold and stored in water at 23 • C ± 2 • C and 95% of humidity until the time of the test. The samples were tested at 1, 3, 7 and 28 days for the compressive strength. Bending test machine is used to divide the specimen into two halves, and each part was subjected to the compressive strength using the compressive testing machine. The layout of the tested sample for exural and compressive strengths are shown in Fig. 2.

Flowability (ASTM C1437)
The owability of cement mortar was determined by using the ow table method as described in ASTM C-1437. After mixing the cement mortar the mixing material was placed in the mold in two layers. Each layer was compacted 25 blows using the rod during the 15 sec. Additional lime content decreased the owability of cement mortar.

Tensile Bonding strength (CIGMAT CT-3, modi ed ASTM C321)
Sandwiched samples were prepared to study the bonding strength according to CIGMAT CT-3 standard [29][30][31]. Different samples were prepared by using concrete brick. The bonding material was cement mortar and cement mortar modi ed with lime content up to 20%. The concrete brick was marked to ensure that the crossed concrete brick is placed in middle and at right the angle to each other. The second brick was placed on the mortar and the oriented correctly. The specimens were allowed to cure at room condition 25 ± 2 • C and 95% of humidity till the time of the test. Samples were tested by subjecting to tensile loading (Fig. 3). Stationary jaws held one brick while the other block was pushed by moving jaws creating a bond force on the bonding.

. Data collection
In this study, more than 500 data were collected from the di erent research studies as summarized in Table 1 to characterize and evaluate the e ect of lime content on the plastic properties such as consistency, owability and setting times and hardened properties such as compressive, tensile bonding and exural strengths of cement mortar. . Modeling

Vipulanandan correlation model
Nonlinear relationships between the compressive strength, owability, setting times and consistency with lime were performed using the Vipulanandan correlation model . The model was proposed as follows: where: Y = Cement mortar property (dependent variable, i.e. consistency, owability and setting time, compressive strength) Yo, A and B = model parameters (Table 6) X = cement mortar property (independent variables, i.e. lime content).

Nonlinear model (NLM)
The compressive strength (σc) and exural strength (σ f ) of cement mortar modi ed with lime (L) was in uenced by the curing time (t) and water-to-cement ratio (w/c %) [35][36][37][38]. The e ects L, t and w/c % of the cement mortar were separated as follows: Compressive strength or exural strength of cement mortar (L=0%) Compressive strength or exural strength of cement mortar modi ed with lime (L ≥ 0%): Based on experimental data and data collected from various research studied in the literature the model parameters (a, b, c, d, e, f, and g) were obtained from multiple regression analysis using the least square method (Table 7).

Results and analyses . Statistical analysis . . Water to cement ratio, (w/c)
Based on the total of 199 of water to cement (w/c) data for the cement mortar collected from the literature (Table 1), the w/c for the cement mortar varied between 0.3 to 0.74% with a mean of 0.47%, the standard deviation of 0.11% and the coe cient of variation (COV) of 23.8 % (Table 4). More than 70 % of the total of w/c of the cement mortar was ranged between 0.4 and 0.6% (Fig. 4(a)). Based on the total of 66 water to binder ratio (w/b) data for the cement mortar modi ed with lime collected from the literature (Table 1), the w/c varied from 0.3 to 0.52% with a mean of 0.44%, the standard deviation of 0.07% and the coe cient of variation (COV) of 17.63 % (Table 4). Almost 85 % of the total of w/c data was ranged between 0.44 and 0.52% (Fig. 4(b)).

. . Lime content, (L (%))
Based on the total 71 lime percent used to modify the cement mortar in the literature, the data varied from 3 % to 45% (by dry weight of cement) with the standard deviation of 11.5 % and the coe cient of variation (COV) of 58%. Almost 70 % of the total of lime content was ranged between 3 % and 20 % (Fig. 5).  (Table 4). Di erent distribution tests for the compressive strength of cement mortar was performed. Based on the Anderson-Darling statistic (AD) and P value (hypothesis testing), Weibull frequency distribution for the compressive strength of cement mortar was observed as shown in Fig. 6(a). 2. Cement mortar modi ed with Lime: A total of 68 compressive strengths (σc) data for cement mortar modi ed with lime were collected from the literature (Table 1), the σc ranged from 6.7 MPa to 65 MPa with a mean of 32.9 MPa, the standard deviation of 16.2 MPa and the coe cient of variation (COV) of 49.1 % ( Table 4). Based on the Anderson-Darling statistic (AD) and P value (hypothesis testing), the probability distribution was Weibull distribution as shown in Fig. 6(b).  (Table 1), the exural strength σ f varied from 2 MPa to 12 MPa with a mean of 7.2 MPa, the standard deviation of 2.58 MPa and the COV of 35 % as summarized in Table 4. In this study, the statistical details and the histograms were performed for each exural strength data set to identify the distribution. Di erent distribution tests for the σ f of cement mortar were performed. Based on the Anderson-Darling statistic (AD) and P value (hypothesis testing), Gamma frequency distribution for the exural strength of cement mortar was selected ( Fig. 7(a)). 4. Cement mortar modi ed with Lime: A total of 25 exural strengths (σ f ) data for cement mortar modied with lime were collected from the literature (Table 1), the exural strength varied from 4 MPa to 11 MPa with a mean of 7.1 MPa while the standard deviation was 1.78 MPa and the coe cient of variation (COV) of 25.3 % as summarized in Table 4. Based on the Anderson-Darling statistic (AD) and P value (hypothesis testing), 3-parameter lognormal Distribution for the exural strength of cement mortar modi ed with lime was selected ( Fig. 7(b)).

Consistency
The consistency of cement decreased as the lime increased. Adding of lime content decreased consistency of cement. The consistency of cement with lime was predicted using Vipulanandan correlation model (Eq. 1). The model parameters, R and RMSE are summarized in Table 6. Adding 20 % of lime decreased the consistency of cement by 6% as shown in Fig. 8(a).

Setting times
Additional of lime accelerate the initial setting time and nal setting time of cement. The variation of initial and nal setting times of cement modi ed with lime was predicted using Vipulanandan correlation model (Eq. 1). The model parameters, the coe cient of determination (R ) and root mean square error (RMSE) are summarized in Table 6. Additional of 20 % of lime decreased the initial and nal setting times by 27% and 16% respectively as shown in Fig. 8(b and c). The reduction could be because of that the lime acts as a nucleation matrix of C-S-H, and accelerates the hydration of cement. Due to the crystal core e ect of lime, the hydration of Tricalcium silicates C S accelerated at an early age [39].

Flowability
The ow table test was conducted to evaluate the effect of lime on the uidity of cement mortar. The uidity of cement decreased as the lime content increased. The variation of ow of cement mortar with lime was predicted using Vipulanandan correlation model (Eq. 1). The model parameters Yo, A, B, R , and RMSE were 108, − . , − . , 0.99 and 0.24 % respectively ( Table 6). Additional of 20 % of lime decreased the uidity of cement mortar by 4 % (Fig. 9). A reduction in the ow of cement mortar could be because of the lime disperses the cement particles more e ciently. The ability of lime is thus probably caused by lower reactivity than cement and less gel formation [40,41].

Compressive strength
The lime decreased the compressive strength (σc) of cement mortar up to 28 days of curing. With the increase in the lime content, the σc of cement mortar is nonlinearly decreased (Fig. 10). The variation of σc versus d L was represented using Vipulanandan correlation model (Eq. 1). The model parameters, R , and RMSE are summarized in Table 6. Additional of 20 % of lime decreased the compressive strength of cement mortar by 20 % at 1 day of curing. Additional of 16 % of lime decreased the σc of cement mortar by 20% at 3 days of curing. Additional of 12 % of lime decreased the σc of cement mortar by 19% at 28 days of curing (Fig. 10). Addition of lime decreased the compressive strength of cement mortar because of the neness of the lime, the lime with large particle has a lower neness than a small particle which cannot ll the void ( lling effect) as a result the strength reduced. The reason lies in the reduction of hydraulically active clinker fraction of cement upon the lime replacement [15]. A multiple linear regres- sion analysis was used to investigate the e ect of lime on the compressive strength of cement mortar, the compressive strength (σc) was correlated to the independent variables such as w/c, curing time and lime using a non-linear relationship (Eq. 2(b)) as shown in Fig. 11. The model parameters were obtained from multiple regression analyses using the least square method (Table 7). Based on the nonlinear model parameter (d= − . ) in Eq. 3 the lime has the highest e ect in decreasing the compressive strength of cement mortar compared to water to cement ratio and curing time.

Flexural strength
Nonlinear Regression Analysis was used to study the e ect of lime on the bending strength (modulus of rupture) of cement mortar, the exural strength (σ f ) was correlated to the independent variables such as w/c, curing time and lime content using a non-linear relationship (Eq. 2(c)) as shown in Fig. 12. The equation parameters were obtained from multiple regression analyses using the least square method (Table 7). Based on the non-linear model parameter (d = − . ) in Eq. 4 the lime has also the highest e ect in decreasing the exural strength of cement mortar compared to water to cement ratio and curing time.    Table 6). The exural strength of cement mortar increased from 4 to 9 MPa when the compressive strength increased from 15 to 45 MPa for cement mortar (Fig. 13).

Tensile bonding strength
The addition of lime decreased the bond strength (σ b ) of cement mortar at 7 days of curing. The variation of σ b and L was represented using the Vipulanandan correlation model (Eq. 1). The model parameters Yo, A, B, the coefcient of determination (R ) and root mean square error (RMSE) were 1.2, − . , − . , 0.99 and 0.01 MPa respectively ( Table 6). The bond strength of cement mortar without lime content was 1.2 MPa at 7 days of curing. Addition of 20% of lime content decreased the bond strength by 131 % (Fig. 14). Di erent type and shape of failure were proposed by CIGMAT CT-3 as summarized in Table 5. The type

Conclusions
The focus of this study was to investigate and quantify the e ect of lime on the setting times, consistency, owability and strengths properties of cement mortar. Based on experimental and collected data the following conclusions are advanced: modi ed with di erent percentage of lime was predicted well as a function of w/c, curing time, lime content. From the NLM parameter e ect of curing time on the CS of cement mortar was much higher than the effect of w/c and lime content. 6. The CS and workability of cement mortar modi ed with di erent percentrage of lime (up to 20%) wa less than unmodi ed cement mortar by 8% and 25% respectivly.