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

1.1 Objectives

The primary objective of this study is to investigate and quantify the effect of lime on the properties of plastic and hardened properties of cement mortar using experimental and collected data from the literature. The specific objectives are as follows:

1. Statistical variations of the compressive and flexural strengths, water to cement ratio and lime content of cement mortar.

2. Investigate the effect of lime on the consistency, setting times, flowability and strength properties of cement mortar.

3. Develop a non-linear relationship to predict the compressive and flexural 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 flexural strengths of the cement mortar modified 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.

2.1 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^′′N45^◦ 26^′08^′′E).

Lime is typically used in the form of quicklime (CaO) or hydrated lime (Ca (OH)₂). Quicklime (CaO) is manufactured by chemical processes that transform calcium carbonate (limestone – CaCO₃) 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 specified in EN 196-1 standard requirements [8, 25].

2.2 Methodology

The plastic and hardened properties of cement mortar modified with lime were tested according to ASTM and BS standard. At least three samples were tested for each condition.

X-ray diffraction (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 reflections (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).

Figure 1

Experimental program presentation of cement mortar modified lime (a) mixing, (b) setting time, (c) cube samples for strength tests (d) flexural test and (e) shape of failure

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 specified 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 final 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 sufficient firmness to resist certain definite pressure (Fig. 1).

Cement mortar preparation (BS EN 196-1:2016)

After mixing the materials, the mortar filled cubic molds with a dimension of (4 x 4 x 16) cm. Themortarput 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 flexural and compressive strengths are shown in Fig. 2.

Figure 2

The layout of cement mortar sample for (a) Flexural test (b) Compression test

Flowability (ASTM C1437)

The flowability of cement mortar was determined by using the flow 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 flowability of cement mortar.

Tensile Bonding strength (CIGMAT CT-3, modified 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 modified 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.

Figure 3

Cement mortar modified with lime under tensile bonding load

2.3 Data collection

In this study, more than 500 data were collected from the different research studies as summarized in Table 1 to characterize and evaluate the effect of lime content on the plastic properties such as consistency, flowability and setting times and hardened properties such as compressive, tensile bonding and flexural strengths of cement mortar.

2.4 Modeling

Vipulanandan correlation model

Nonlinear relationships between the compressive strength, flowability, setting times and consistency with lime were performed using the Vipulanandan correlation model [32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54]. The model was proposed as follows:

where:

Y = Cement mortar property (dependent variable, i.e. consistency, flowability and setting time, compressive strength)

Y_o, A and B = model parameters (Table 6)

Table 5

Failure Types according to CIGMAT CT 3 standard [29, 31]

Failure Type	Description	CIGMAT CT 3 Test
Type 1	Substrate Failure
Type 2	Mortar Failure
Type 3	Bonding Failure
Type 4	Bonding and Substrate Failure
Type 5	Bonding and Mortar Failure

X = cement mortar property (independent variables, i.e. lime content).

Nonlinear model (NLM)

The compressive strength (σ_c) and flexural strength (σ_f) of cement mortar modified with lime (L) was influenced by the curing time (t) and water-to-cement ratio (w/c %) [35, 36, 37, 38]. The effects L, t and w/c % of the cement mortar were separated as follows:

Compressive strength or flexural strength of cement mortar (L=0%)

Compressive strength or flexural strength of cement mortar modified 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).

3.1 Statistical analysis

3.1.1 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 coefficient 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 modified 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 coefficient 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)).

Figure 4

Histogram of the water to cement ratio (w/c) for (a) cement mortar and (b) cement mortar modified with lime used in the literature

3.1.2 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 coefficient of variation (COV) of 58%. Almost 70 % of the total of lime content was ranged between 3 % and 20 % (Fig. 5).

Figure 5

Histogram of percent of lime used in the literature

3.2 Mechanical properties

Compressive strength

1. Cement mortar: A total of 318 compressive strengths (σ_c) data for the cement mortar collected from the literature (Table 1) the compressive strength (σ_c) of the cement mortar up to 28 days of curing ranged from 3 MPa to 65 MPa with a mean of 30 MPa, the standard deviation of 12 MPa and the coefficient of variation (COV) of 40 % (Table 4). Different 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).

   

   Figure 6

   Statistical distribution of the compressive strength for (a) cement mortar and (b) cement mortar modified with lime up to 28 days of curing

2. Cement mortar modified with Lime: A total of 68 compressive strengths (σ_c) data for cement mortar modified with lime were collected from the literature (Table 1), the σ_c ranged from 6.7 MPa to 65 MPa with a mean of 32.9 MPa, the standard deviation of 16.2 MPa and the coefficient 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).

3.3 Flexural strength

3. Cement mortar: Based on a total of 43 flexural strengths (σ_f ) data for cement mortar up to 28 days of curing were collected from the literature (Table 1), the flexural 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 flexural strength data set to identify the distribution. Different 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 flexural strength of cement mortar was selected (Fig. 7(a)).

   

   Figure 7

   Statistical distribution of the flexural strength for (a) cement mortar and (b) cement mortar modified with lime up to 28 days of curing

4. Cement mortar modified with Lime: A total of 25 flexural strengths (σ_f ) data for cement mortar modified with lime were collected from the literature (Table 1), the flexural 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 coefficient 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 flexural strength of cement mortar modified with lime was selected (Fig. 7(b)).

3.4 Property correlation

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, R² and RMSE are summarized in Table 6. Adding 20 % of lime decreased the consistency of cement by 6% as shown in Fig. 8(a).

Figure 8

Relationship between percentage of lime and (a) Consistency (b) Initial setting time and (c) Final setting time of cement paste

Setting times

Additional of lime accelerate the initial setting time and final setting time of cement. The variation of initial and final setting times of cement modified with lime was predicted using Vipulanandan correlation model (Eq. 1). The model parameters, the coefficient of determination (R²) and root mean square error (RMSE) are summarized in Table 6. Additional of 20 % of lime decreased the initial and final 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 effect of lime, the hydration of Tricalcium silicates C₃S accelerated at an early age [39].

Flowability

The flow table test was conducted to evaluate the effect of lime on the fluidity of cement mortar. The fluidity of cement decreased as the lime content increased. The variation of flow of cement mortar with lime was predicted using Vipulanandan correlation model (Eq. 1). The model parameters Yo, A, B, R², and RMSE were 108, −0.96, −0.05, 0.99 and 0.24 % respectively (Table 6). Additional of 20 % of lime decreased the fluidity of cement mortar by 4 % (Fig. 9). A reduction in the flow of cement mortar could be because of the lime disperses the cement particles more efficiently. The ability of lime is thus probably caused by lower reactivity than cement and less gel formation [40, 41].

Figure 9

Relationship between lime content and of flowability of cement mortar

Compressive strength

The lime decreased the compressive strength (σ_c) of cement mortar up to 28 days of curing. With the increase in the lime content, the σ_c of cement mortar is nonlinearly decreased (Fig. 10). The variation of σ_c versus d L was represented using Vipulanandan correlation model (Eq. 1). The model parameters, R², 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.

Figure 10

Relationship between Lime content and compressive strength of cement mortar at different curing times (a) 1day (b) 3 days (c) 7 days and, (d) 28 days of curing

Additional of 16 % of lime decreased the σ_c of cement mortar by 20% at 3 days of curing. Additional of 12 % of lime decreased the σ_c 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 fineness of the lime, the lime with large particle has a lower fineness than a small particle which cannot fill the void (filling 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 regression analysis was used to investigate the effect of lime on the compressive strength of cement mortar, the compressive strength (σ_c) 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= −0.27) in Eq. 3 the lime has the highest effect in decreasing the compressive strength of cement mortar compared to water to cement ratio and curing time.

Figure 11

Comparison between measured and predicted of compressive strength for cement mortar modified with lime

Flexural strength

Nonlinear Regression Analysis was used to study the effect of lime on the bending strength (modulus of rupture) of cement mortar, the flexural 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 = −0.04) in Eq. 4 the lime has also the highest effect in decreasing the flexural strength of cement mortar compared to water to cement ratio and curing time.

Figure 12

Comparison between measured and predicted of flexural strength for cement mortar modified with lime

The Relationship between compressive strength (σ_c) and flexural strength (σ_f) of cement mortar modified with lime

Based on the total of 24 experimental cement mortar data modified with lime content. The variation of σ_f and σ_c was represented using the Vipulanandan correlation model (Eq. 1). The model parameters Y_o, A, the coefficient of determination (R²) and root mean square error (RMSE) were 0.969, 5.84, 0.93 and 0.49 MPa respectively (Table 6). The flexural 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).

Figure 13

Relationship between compressive and flexural strength of cement mortar modified with lime

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 Y_o, A, B, the coefficient of determination (R²) and root mean square error (RMSE) were 1.2, −8.95, −1.05, 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). Different type and shape of failure were proposed by CIGMAT CT-3 as summarized in Table 5. The type of failure between the mortar and concrete bricks were type 2 failure based on CIGMAT CT-3 standard [29, 31] as shown in Fig. 15.

Figure 14

Relationship between percentage of Lime and tensile bonding strength of cement mortar at 7 days of curing

Figure 15

Typical tensile bonding failure for cement mortar modified with lime