Influence of pozzolanic materials on the properties of natural hydraulic lime based mortars

Construction and Building Materials 244 (2020) 118360

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Influence of pozzolanic materials on the properties of natural hydraulic lime based mortars Dajiang Zhang a, Jihui Zhao b,c,d,⇑, Dongmin Wang a,⇑, Yiren Wang b, Xiangdong Ma a a

China University of Mining & Technology, Beijing 100083, China School of Civil Engineering, Sun Yat-sen University, Guangzhou 510275, China c Guangdong Key Laboratory of Oceanic Civil Engineering, Guangzhou 510275, China d Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519082, China b

h i g h l i g h t s
Slag powder and silica fume have positive effect on the mechanical property of NHL based mortar.
Pozzolanic materials can improve the environmental resistance of NHL based mortar effectively.
The hydration reaction of NHL based mortars can be promoted by both slag powder and silica fume.
The hardened products and their existential forms of NHL, S-NHL and F-NHL mortars are different.

a r t i c l e

i n f o

Article history: Received 18 September 2019 Received in revised form 7 January 2020 Accepted 4 February 2020

Keywords: Natural hydraulic lime Pozzolanic materials Mechanical properties Environmental resistance properties Micro-morphology

a b s t r a c t To evaluate the influence of pozzolanic materials (slag powder and silica fume) on the properties of natural hydraulic lime (NHL) based mortars, the properties of NHL mortar, slag powder-NHL based mortars (S-NHL) and silica fume-NHL based mortars (F-NHL) were studied deeply from the aspect of physical and mechanical properties, environmental resistance properties, hardening reaction process and micro morphology in this paper, among which S-NHL are prepared with 10% and 20% slag powder to substitute NHL and F-NHL are prepared with 10% and 20% silica fume to substitute NHL, respectively. The results indicate that the NHL mortars have preferable fluidity compared to the S-NHL and F-NHL mortars. In terms of mechanical properties, the compressive strength of S-NHL and F-NHL mortars have been significantly improved, among which the compressive strength of S20-NHL and F20-NHL mortars reached 7.73 MPa and 7.99 MPa at 28 days, respectively. The environmental erosion resistance of S-NHL and F-NHL mortars have been improved by a proportion of NHL is replaced by pozzolanic materials; moreover, the addition of slag powder has a more significant improvement on the sulfate resistance of mortars, and the acid resistance of mortars are improved obviously by the addition of silica fume. The pozzolanic materials and Ca(OH)2 occur pozzolanic reaction with water and produce more calcium silicate (aluminate) hydrate (C-S(A)-H), and CaCO3 crystals are formed by carbonization reaction in mortar and interweave with hydration products to fill in the air pores of mortar, thereby the micro-structure of mortars have ameliorated, the performance of S-NHL and F-NHL mortars are improved finally. The pozzolanic index P show that the pozzolanic effect of silica fume is higher than slag powder at the early stage (before 28 days) of NHL based mortar hardening, and slag powder is higher than silica fume at the later stage (after 28 days), meanwhile slag powder has better effect for improving the compressive strength of mortar compared to silica fume. Ó 2020 Elsevier Ltd. All rights reserved.

1. Introduction Heritage of ancient buildings and historical record revealed that hydraulic mortar was prepared by mixing lime and pozzolan ⇑ Corresponding authors. E-mail addresses: [email protected], [email protected] (J. Zhao), [email protected] (D. Wang). https://doi.org/10.1016/j.conbuildmat.2020.118360 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved.

materials, and that was used to build all kinds of buildings in ancient Rome and ancient Greece [1]. Since the 18th century, people began to study the hydraulic characteristics of cementitious materials. In 1756, Smeaton discovered that the hydraulic lime could be obtained by the limestone composed of moderate clay after being calcined. In 1812, Vicat confirmed that the hydraulic properties of these cementitious materials were the result of burning limestone and clay continuously, the cement was invented

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D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

by J. Aspin in 1842, and since the late 19th century, Portland cement and its derivatives become the overriding cementitious materials due to their standardization of production in the field of construction industry [2]. Cement have the properties of fast setting and hardening, good water resistance and high strength, however, since the 1980s, with the requirements of people increasing for the protection and repairation of ancient cultural relics and historical buildings, cement and other cementitious materials have been compared. The problems have gradually emerged that poor durability of cement and worse compatibility of other cementitious materials [3], people re-recognize the out-bound cementitious materials (hydraulic lime). Natural hydraulic lime (NHL) is ‘‘a lime with hydraulic properties produced by burning of more or less argillaceous or siliceous limestone (including chalk) with reduction to powder by slaking with or without grinding” according to BS EN 459-1 [41]. The mineralogical phases of NHL mainly have calcium silicate (C2S), calcium hydroxide (Ca(OH)2), calcite (CaCO3). As a hydraulic cementitious material, NHL has both hydraulicity and air hardening properties, which is usually used to prepare the adhesive, surface or tick off seam mortars, and it is widely used in the fields of the external wall decoration mortar engineering and ancient building repair materials. The hardening process of NHL mainly through the hydraulic phase (C2S) that take place hydration reaction in the water environment and forms calcium silicate hydrate (C-S-H), while calcite (CaCO3) crystals are formed by the reaction of Ca (OH)2 and CO2 in the air under the action of water. NHL have moderate mechanical strength, suitable hardening speed (4–12 h) and good water vapor permeability. Relevant research show that during the repairation of ancient buildings, NHL repair mortar is produced by NHL, quartz sand and other materials, it have high compatibility with ancient buildings about the physical, chemical and mechanical properties [3–7], and it was found that soluble salt will not be introduced into the structural materials after repair the ancient building by using the NHL repair mortar [8,35]. These advantages of NHL have prompted its heavy use in the repairation of ancient buildings and external wall decoration mortar engineering, moreover, with recovering of hydraulic lime applications, the demand is increasing, and the production of NHL is improving year by year. Meanwhile, hydraulic lime (commonly known as artificial hydraulic lime) prepared by mixing an appropriate amount of pozzolanic materials into aerial lime have also been used gradually. Hydraulic lime (HL) in European Standard BS EN 459-1 [41] is defined as ‘‘a binder consisting of lime and other materials such as cement, blast furnace slag, fly ash, limestone filler and other suitable materials. It has the property of setting and hardening under water. Atmosphere carbon dioxide contributes to the hardening process”. Formulated Lime (FL) is defined as ‘‘a lime with hydraulic properties mainly consisting of air lime (AL) and/or natural hydraulic lime (NHL) with added hydraulic and/or pozzolanic material. It has the property of setting and hardening when mixed with water and by reaction with carbon dioxide from the air (carbonation)”. It is mentioned in the standard that pozzolanic materials can be used as an important component of hydraulic lime. BS EN 197-1 [43] stipulates ‘‘Pozzolanic materials are natural substance of siliceous or silico-aluminous composition or a combination thereof”. Pozzolanic materials react at normal ambient temperature with dissolved calcium hydroxide (Ca(OH)2) to form strength-developing calcium silicate and calcium aluminate compounds. Currently, a large quantity of pozzolanic materials (such as fly ash, slag powder and others) have been produced in industrial production process, which can be used as SCMs in cement concrete. The composite mortars are prepared with pozzolanic material and NHL as cementitious material, its have great feasibility and desirability in both environmental improvement and sustainable production, and reduce environmental pollution and

save massive mineral resources [9,10], because of the superiority of NHL in the field of ancient buildings repair, with the increasing of NHL demand, the production of NHL will be promoted, in the meantime, energy and resources are consumed, carbon dioxide (CO2) and harmful dust also be generated in large quantities [11], but it is an effective way to improve the sustainability of building mortar and concrete by the replacement of partial cementitious materials with pozzolanic materials [12,13]. Slag powder and silica fume are two kinds of pozzolanic materials produced by smelting process, the chemical components mainly are a lot of active silica (SiO2) or/and active aluminium oxide (Al2O3), which are basically consistent with natural pozzolana of ancient buildings, otherwise, slag powder and silica fume have not hydraulicity, but there have pozzolanic reaction after they mixed with NHL, and the hydraulicity of NHL can be improved within limits, so its application in hydraulic lime are beneficial to compatibility with ancient buildings materials and have great application potential [16,19,24]. Plenty of research shows that slag powder replace part of cement can improve the performance of mortar and reduce the amount of cement to some extent, the use of cement is reduced that can bring good results for economic and environmental effects [14–17]. As pozzolanic material, silica fume is added into cement concrete that have good pozzolanic effect and fine particle filling effect, it can effectively enhance the structural compactness of mortar, and the strength, impervious performance and chemical erosion resistance of cement mortar and concrete can be improved [18–23]. Currently, many researchers have found some problems for NHL using process, such as the relatively poor environmental resistance (especially the acid erosion resistance, alkali resistance and sulfate resistance) [10,24–29]. Pozzolanic material-NHL based cementitious materials occur pozzolanic reaction with water and carbonization reaction continuously, these processes can be expressed by the chemical reaction formulas (1)–(4):

2CaOSiO2 + nH2 O ! mCaOSiO2 kH2 O + (2-m)Ca(OH)2

ð1Þ

xCa(OH)2 + SiO2 + nH2 O ! mCaOSiO2 (x + n)H2 O

ð2Þ

xCa(OH)2 + Al2 O3 + nH2 O ! mCaOAl2 O3 (x + n)H2 O

ð3Þ

Ca(OH)2 + CO2 + nH2 O ! CaCO3 + (n + 1) H2 O

ð4Þ

the hydration reaction of NHL can be improved by using pozzolanic material, meanwhile the uncarbonized Ca(OH)2 dehydrate and recrystallize in dry environment, so that a compact structure is formed with C-S(A)-H to further improve environment resistance properties. For another, both slag powder and silica fume are industrial by-products that come from a wide range of sources, and replacing part of NHL not only reduce the impact of NHL production on resource and environment, but also realize the resource utilization of industrial waste residue. Thus, the application of slag powder, silica fume and other pozzolanic materials in NHL have an important development prospect, and have an essential positive significance for the sustainability of hydraulic lime. The purpose of this work is to prepare preferable mortars by mixing pozzolanic materials that have better performance and suitable for restoration of ancient buildings. Therefore, an intensive study of the properties of NHL, S-NHL and F-NHL mortars with regarding to physical and mechanical properties, environment resistance properties, hydration and hardening process, microstructure were performed. The rational mechanism about the improvement of properties were raised and discussed, and the feasibility of using pozzolanic materials in NHL based mortars was evaluated.

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D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

2. Materials and experimental methods 2.1. Raw materials Natural hydraulic lime (NHL2), slag powder and silica fume as the raw materials were used in the experiments. NHL2 was supplied by the Saint-Astier company, France, and main mineral phases include dicalcium silicate (C2S), calcium hydroxide (Ca (OH)2), calcite (CaCO3) and quartz, as shown by the results of Xray diffraction analysis presented in Fig. 1. Slag powder is mainly composed of calcium akermanite and gehlenite, mineral phases of silica fume mainly exist in the form of amorphous SiO2. The chemical compositions of the raw materials were determined by X-ray fluorescence and results listed in Table 1. The sand used in the mortar mixtures was natural sand, the range and proportion of particle size distribution were measured as shown in Fig. 2. Fig. 2. The size distribution of quartz sand particle.

2.2. Experimental methods 2.2.1. Preparation and curing of lime mortars Study on the three kinds of NHL based mortars were prepared respectively in the experiment: NHL mortar (Control), slag powder-NHL based mortars (Series-I) and silica fume-NHL based mortars (Series-II). Natural hydraulic lime of NHL2 was used as the cementitious materials of Control mortar, denote as NHL. The partial NHL2 was substituted by 10% and 20% slag powder respectively as the cementitious material to prepare mortar samples, denote as S10NHL and S20-NHL respectively. The partial NHL2 was substituted by 10% and 20% silica fume respectively as the cementitious material to prepare mortar samples, denote as F10-NHL and F20-NHL respectively. According to Chinese Standard GB/T 17671-1999 [44] and Chinese Standard JC/T 681-2005 [45], the mixer for mixing mortars of ISO is used to prepare mortar samples, and the mixing procedure is as follows: First, the required water is added to the stirring pot, and secure the stirring pot after adding the mixture. Then, Start the machine and stir at low speed (140 ± 5 r/min) for 30 s, and add the sand evenly into stirring pot while starting the second 30 s.

After adding the sand, turn the machine to high speed and stir for another 30 s. Stop mixing for 90 s, and in the first 15 s, scrape the mortar of blade and on the pot wall into the middle of the pot. Last, stirring at high speed (285 ± 10 r/min) for 60 s continually. The time error of each stirring stage should be within ±1 s. The mortar samples were molded in prismatic casts with a size of 40  40  160 mm and de-moulded 72 h later, the water consumption of mortars according to European standard BS EN 459-2 [42], and the mix proportion of mortars were presented in Table 2. Curing was conducted in a constant temperature humidity conditions (22 ± 3°C and RH 60%) for fixed periods (14, 28, 90,180 days). 2.2.2. Measurement of physical and mechanical properties of mortars (i) The flow of all mortars were tested by NLD-3 cement mortar fluidity determinator according to Chinese Standard GB/T 2419-2005 [46]; (ii) The water absorption of the mortars was measured according to Chinese Standard JGJ/T 70-2009 [47], meanwhile the total volume and mass of mortars were measured after curing 28 days, and then the apparent density was achieved. (iii) The techniques used were KZJ-5000 cement electric bending test machine for the flexural test (load rate: 50 N/s) and servo material pressure testing machine for the compressive test (load rate: 200 N/s), respectively. They were evaluated according to China Standard GB/T 17671-1999 [44] and BS EN1015-11 [50]. 2.2.3. Environmental erosion resistance properties of lime mortars test According to the literatures [24,27], the environmental erosion resistance properties of mortars were evaluated by acid resistance and sulfate resistance, respectively. (i) Acid erosion resistance. Acid erosion resistance was performed on the mortars after curing 28 days. Two methods were used to evaluate the influence of 0.1 mol/L hydrochloric acid (HCl) solution on damage to the mortars. First method was based on weight variation of mortar samples

Fig. 1. X-ray diffraction patterns of NHL2.

Table 1 Chemical composition of the raw materials (%). Raw materials

CaO

SiO2

Fe2O3

Al2O3

MgO

K2O

SO3

Na2O

NHL2 Slag powder Silica fume

79.66 36.26 0.72

7.90 35.03 86.73

1.52 0.63 2.50

2.56 14.95 0.59

6.18 9.31 2.18

0.71 0.38 1.91

0.92 1.13 1.15

0.08 0.12 1.83

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D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

Table 2 Mix proportions of NHL based mortars. Material/g

NHL2 Slag powder Silica fume Natural sand Water

Control

Series-I

Series-II

NHL

S10-NHL

S20-NHL

F10-NHL

F20-NHL

550

495 55

440 110

495

440

1100 330

1100 330

1100 330

55 1100 330

110 1100 330

(40  40  160 mm) before and after immersing in HCl solution, the weight of mortar samples was measured after immersing for 14 and 28 days respectively, and the weight variation was calculated by Eq. (5). Another method depended on the compressive strength (CS) variation of mortar samples before and after immersing in HCl solution for 28 days, the CS variation were calculated by Eq. (6). In the process of experiment, the pH value of HCl solution (0.1 mol/L) was measured during the immersion, when the pH value reached 4 the solution was refreshed.

x¼

C1  C0  100% C0

S1  S0  100% S0

Discontinued the hydration of samples by anhydrous alcohol, ground and sieved 80 lm mesh, and dried to constant weight in a vacuum environment. Thermogravimetric analysis of the samples was carried out by TG-DTA6300 measurements at the heating rate of 10 °C/min under the protection of an N2 atmosphere, and the temperature range was 30–850 °C. (ii) SEM test of samples

ð5Þ

where x is the weight variation of mortar samples (%), and C0 is weight of mortar samples before immersing in HCl solution (g), C1 is weight of mortar samples after immersing in HCl solution (g). *x is positive value indicates that the increase of mortar samples weight, while x is negative value indicates the loss of mortar samples weight.

u¼

(i) TG-DTA analysis of samples

ð6Þ

where u is the CS variation of mortar samples (%), and S0 is CS of mortar samples before immersing in HCl solution (MPa), S1 is CS of mortar samples after immersing in HCl solution (MPa). *u is positive value indicates that the CS of mortar samples is increased, while u is negative value indicates that the CS of mortar samples is reduced. (ii) Sulfate resistance. Sulfate resistance was performed on the mortar samples (40  40  160 mm) after curing 28 days. The mortar samples were immersed in Na2SO4 solution (10% w/w), the weight of mortar samples was measured after immersing for 14 days and 28 days respectively, and the CS of mortar samples were measured after immersing for 28 days. The solution was refreshed every week during the test. The CS of mortar samples was measured after 28 days of immersion, and the change rate of CS was calculated. Calculation method of mortar samples weight variation and CS variation before and after immersing Na2SO4 solution refer to the Section 2.2.3(i). The mortar samples surface was observed by immersing and recorded the condition of appearance regularly. 2.2.4. Isothermal calorimetry test of lime pastes The hydration kinetics of hydraulic lime was measured by an eight-channel isothermal calorimeter (Thermometrics TAM air) in all NHL-based pastes with a w/b (water/binder ratio) of 1.0. The temperature and humidity of testing environment were constant 25°C and 60% respectively.

The samples of each curing period were treated as specimens of a thin sheet with a size of 5  5 mm2 approximately. The hydration of samples was discontinued by anhydrous alcohol, and these specimens were dried to constant weight in a vacuum environment at 65 °C; then, after spraying gold onto the surface of the specimens, the morphologies of specimens were observed by scanning electron microscopy (Hitachi SU8000). 2.2.6. Evaluation of pozzolanic effect Yu et al. [30] researched that the pozzolanic effect of pearlite powder on the concrete, and Xu et al. [24] studied the pozzolanic effect of diatomite and fly ash used in the NHL-based mortars, thus the pozzolanic strength index was calculated according to the works. Specific strength ratio (R) is defined a ratio of the contributions to mortar strength from unit NHL and unit pozzolanic material, and it is expressed by the Eq. (7):

R ¼ f=q

ð7Þ

where, f is the compressive strength of mortar (MPa), q is the NHL or pozzolanic material percentage of the cementitious materials. RC expresses the contribution of unit NHL mortar compressive strength without any mineral admixture, while RM expresses the contribution of unit pozzolanic material to mortar compressive strength, and RP is the contribution of the pozzolanic effect to mortar compressive strength due to mineral admixture, is expressed by the Eq. (8):

RP ¼ RM  RC

ð8Þ

K is the ratio of RM to RC, and it can be calculated by the Eq. (9):

K ¼ RM =RC

ð9Þ

P is the percentage value of the contribution of pozzolanic effect to mortar compressive strength, and it can be written as Eq. (10):

P ¼ ðRP =RM Þ  100%

ð10Þ

3. Results and discussion 3.1. Main physical properties of mortars

2.2.5. The test of hydration and hardening properties of samples Reaction degree and morphology of products of NHL-based pastes were measured by thermogravimetric-differential thermal analysis (TG-DTA) and scanning electron microscope (SEM), respectively.

Table 3 gives the basic properties and standard deviation of fresh and hardened mortars, it can be seen that the flow of S-NHL mortars in fresh state decreased with the addition of slag powder, and the diminution of flow along with the addition of slag

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D. Zhang et al. / Construction and Building Materials 244 (2020) 118360 Table 3 Basic properties and standard deviation of fresh and hardened mortars. Samples

Flow (mm)

SD

Apparent density (g/cm3)

SD

Water absorption (%)

SD

NHL S10-NHL S20-NHL F10-NHL F20-NHL

204 198 194 187 180

5.57 2.45 3.61 3.46 4.58

1.79 1.81 1.84 1.72 1.77

0.026 0.017 0.035 0.02 0.026

17.31 17.21 16.89 19.40 18.14

0.087 0.056 0.053 0.122 0.096

SD: Standard Deviation,

rðrÞ, rðrÞ ¼

sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi n P 1  2. ðxi  XÞ n1

i¼1

powder dosage. This is due to the loose and porous irregular structure of the slag powder, which have not a ball effect [36]. The flow of mortars were reduced greater degree by silica fume as well, and the flow of F10-NHL and F20-NHL fresh mortars were decreased by 8.3% and 12.25% compared with the NHL fresh mortar, for one thing, because the particle size (0.1–1 lm) of silica fume is small and the specific surface area was large, so it had a major water demand, for another that the amorphous SiO2 content of silica fume was very large and had high activity, it reacted with Ca (OH)2 took place in a short time relatively and the C-S-H with low Ca/Si ratio was produced, bring about the increase of mortar viscosity and the decrease of flow [37]. The apparent density of S-NHL mortars was increased slightly, while the F-NHL mortars were decreased, which was due to the different density between slag powder, silica fume and NHL2 (the density of slag powder, silica fume and NHL2 are 2.92 g/cm3, 2.23 g/cm3 and 2.66 g/cm3, respectively). The water absorption of S-NHL and F-NHL mortars were slightly different from NHL mortar, the use of silica fume had a greater influence on the water absorption of NHL based mortars compared with slag powder.

of S10-NHL and S20-NHL mortars at 28 days reached 5.61 MPa and 7.73 MPa, respectively, while the decrease of FS along with the addition of slag powder dosage, and the FS of S-NHL mortars at the same curing ages have a reducing to varying degrees. The growth of CS of F-NHL mortars also along with the addition of silica fume dosage and the extension of curing ages, the early strength increased rapidly and the growth of later strength was slow relatively, it was attribute to silica fume contained a large number of amorphous SiO2 with higher activity and reacted with Ca(OH)2 of mortars to produce plenty of C-S-H [38], which made the early strength of F-NHL mortars had a rapid increase relatively. The CS of F10-NHL and F20-NHL mortars at 28 days raised 169% and 227% compared with NHL mortar severally. The growth of FS along with the addition of silica fume dosage, but it had a reducing obviously compared with NHL mortar. Overall, the early CS of NHL based mortars had a better improvement by silica fume substitute partial NHL, and the strengthening effect of slag powder on the later CS of NHL based mortars were more obvious.

3.2. Mechanical properties of mortars

3.3.1. Acid erosion resistance Fig. 4 shows the surface images of NHL based mortar samples before and after immersing 28 days in HCl solution. The alkaline substances (Ca(OH)2 and CaCO3) of mortars were easily affected by acidic compounds, the main cause of mortar damage was the chemical reaction between the two [24]. During the HCl erosion test, there were lots of bubbles generated on the mortar surface at the beginning, and the phenomenon of bubble formation was no longer obvious with the increasing of immersing time. Judging from the surface condition of each mortars, the damage effect of HCl erosion on NHL mortar and S10-NHL mortars were the worst. The weight variation of mortars after immersing in HCl solution is presented in Table 4. It shows that the weight variation of NHL

Fig. 3 shows the compressive strength (CS) and flexural strength (FS) of all NHL based mortars at curing period of 14, 28, 90 and 180 days, and fit the strength change of with the curing ages. The results show that the strengthening effect of silica fume on the early CS of NHL based mortars (before 28 days) was slightly higher than slag powder, while the strengthening effect of slag powder on the later CS of NHL based mortars (after 28 days) was higher than silica fume. The CS of NHL mortar is 2.44 MPa at 28 days, and S-NHL mortars of all curing ages had a higher CS compared with NHL mortar [16], the growth of CS along with the addition of slag powder dosage and the extension of curing age, the CS

3.3. Environmental erosion resistance properties of mortars

2.0

14

Y=1.815-1.818e -x/25.602,R2=0.999 -x/29.373

Y=12.062-12.082e

12

,R =0.991

1.6

Y=10.402-10.397e-x/19.763,R2=0.985

10 F20-NHL

Flexural Strength(MPa)

Compressive strength(MPa)

S20-NHL

2

Y=9.074-9.119e-x/32.334,R2=0.986

S10-NHL

8

Y=7.843-7.943e-x/18.813,R2=0.0.969 F10-NHL

6 4 Y=3.592-3.583e-x/25.081,R2=0.995

NHL S10-NHL

1.2

Y=1.472-1.483e -x/20.328,R2=0.991 Y=1.271-1.256e -x/29.701,R2=0.994 Y=1.222-1.223e -x/13.278,R2=0.990

S20-NHL

F20-NHL 0.8

F10-NHL

Y=0.880-0.876e -x/12.163,R2=0.990

0.4

NHL

2

0.0

0 0

20

40

60

80

100

Curing age(days)

120

140

160

180

0

20

40

60

80

100

120

Curing age(days)

Fig. 3. Compressive and flexural strength of lime mortars after various curing ages and its fitting curves.

140

160

180

6

D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

Fig. 4. External patterns of mortars ((a): Before being immersed in HCl solution; (b): After being immersed in HCl solution for 28 days).

Table 4 Weight variations of mortars after being immersed in HCl and Na2SO4 solution. Mortar

Aggressive environment

NHL S10-NHL S20-NHL F10-NHL F20-NHL

HCl, 0.1 mol/L

Weight variation (%) 14 d

28 d

2.78 0.89 1.76 1.84 1.50

3.31 2.04 2.47 2.73 1.82

mortar immersed for 14 days and 28 days all were highest. The CS and CS variation before and after mortars were immersed in HCl solution are shown in Fig. 5, here we can see that the CS of SNHL and F-NHL mortars after HCl erosion are larger than NHL mortar, and the CS of S10-NHL and F10-NHL mortars were decreased by HCl erosion obviously, nevertheless, the CS of S20-NHL and F20-NHL mortars had growth moderately, meanwhile the CS of NHL mortar had a maximum reduction. The main reason for these results were that slag powder and silica fume to substitute partial NHL, for one thing, the content of Ca(OH)2 and CaCO3 of mortars can be reduced, another, slag powder and silica fume occurred pozzolanic reaction by reacting with Ca(OH)2, and the CaCO3 formed by carbonization of Ca(OH)2 will also be reduced. Generally speaking, the acid erosion resistance of NHL based mortars can be improved by mixing a certain amount of slag powder or silica fume, and the improvement of acid erosion resistance along with the increasing of slag powder and silica fume content.

Compressive strength before acid corrosion Compressive strength after acid corrosion Compressive strength variation percentages

10

50 40 30

8 20 6

10 0

4

-10

2

S trength variation percentages (% )

Compressives trength of mortars before and after acid corrosion(MPa)

12

-20 0 NHL

S10-NHL

S20-NHL

F10-NHL

Aggressive environment

F20-NHL

Fig. 5. Compressive strength and strength variation before and after mortars were immersed in HCl solution.

Na2SO4, 10% w/w

Weight variation (%) 14 d

28 d

3.74 2.80 3.22 1.71 1.52

5.96 3.31 3.59 2.89 2.92

3.3.2. Sulfate resistance Fig. 6 shows the surface damage images of all NHL-based mortar samples after immersing 28 days in Na2SO4 solution, there occurred severe expansive crack in NHL mortar (the biggest crack size reaches 2941.2 lm), result in that it lost workability completely [27], the process of destruction was the formation of gypsum by the reaction of Ca(OH)2 and sulfate ion (SO24 ) primarily. Secondly, when the sulfate ion transport into the matrix and the concentration reaches supersaturation, it will precipitate out and form sulfate crystals, and sodium sulfate crystals will grow with the increasing of supersaturation, leading to the expansion and cracking of mortars [40]. There were many dilatant cracks on the S10-NHL mortar surface (the size of dilatant cracks less than 423.7 lm), few cracks are small and unclear relatively on the S20-NHL mortar surface (the cracks size less than 196.1 lm), the surface of F-NHL mortars had a good condition and no obvious cracks occurred. These phenomena may be due to the mixed part of slag powder in S-NHL mortar, amorphous Al2O3 and Ca(OH)2 took place the pozzolanic reaction to form C-A-H (mCaOAl2O3nH2O), and the gypsum was generated by the SO24 reacted with Ca(OH)2, then the gypsum reacted with C-A-H to form ettringite [16,24], thereby the volume of hardened mortars was increased and the considerable crystallization pressure was produced, resulting in expansion, dehiscence and destruction of mortars, its equations are as follows: Ca(OH)2 + Na2SO4 + 10H2O ? CaSO42H2O + 2NaOH, C-A-H + CaSO42H2O + H2O ? Ettringite + Ca(OH)2 [48,49]. However, due to the lower content of slag powder in S-NHL mortars, the amount of C-A-H generated by hydration is small, hence the expansion stress formed by ettringite has limited destroy to mortar. With the increasing of slag powder content, the sulfate resistance of S-NHL mortars was improved obviously, and the sulfate resistance of F-NHL mortars were greatly improved by silica fume to substitute partial NHL [31]. Fig. 7 presents the schematic diagram of erosion and destruction process of NHL based mortars in sulfate solution. According to the above study on sulfate resistance, NHL based mortars are destroyed by sulfate ion in two ways mainly: i) sulfate reacts with

D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

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Fig. 6. Damage condition of mortars after being immersed in Na2SO4 solution for 28 days.

Fig. 7. Schematic diagram of erosion and destruction process of NHL based mortars in sulfate solution.

Ca(OH)2 and other basic compounds to form gypsum and ettringite in mortar; ii) sodium sulfate solution gathering and crystal growing in the matrix, and when the crystal grows to a certain extent, it will produce expansive stress on the surrounding pore wall.

Table 4 shows weight variation of mortars after immersing in Na2SO4 solution, and weight variation (+) of S-NHL and F-NHL mortars were smaller than NHL mortar. The CS and CS variation before and after mortars were immersed in Na2SO4 solution were shown

D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

in Fig. 8, NHL mortar lost the mechanical strength completely, nevertheless, the CS of S-NHL and F-NHL mortars enhanced to a certain extent, the CS variation (+) of mortars were increased with the increasing of slag powder and silica fume content. It can be concluded that the addition of slag powder and silica fume can effectively improve the sulfate resistance of NHL-based mortars, and silica fume had more obvious improvement to sulfate resistance of NHL based mortars compared with slag powder, there are two reasons about the improvement to sulfate resistance, on one hand, the content of portlandite of NHL based mortars are reduced by replacing part of NHL with pozzolanic materials, on the other, more hydration products are produced by the reaction of slag powder/ silica fume and portlandite. 3.4. Hydration heat release characteristics of NHL based pastes The hydration heat release curves of NHL, S-NHL and F-NHL pastes are shown in Fig. 9. In the early hydration period of less than 0.5 h, the exothermic peak of all NHL based pastes were very high, and the heat release of this stage was due to the rapid dissolution of the mineral phases (Ca(OH)2, C2S, silicate phase and aluminosilicates) in contact with water, after that, the heat release rate of hydration was reduced and leveling out, and the hydration becoming inducing age [33]. Each NHL based pastes entered the hydration acceleration period about 6 h and began to form the second

90 80

12

70

10

60 50

8

40 6 30 4

20

2

10 0

0 NHL

S10-NHL

S20-NHL

F10-NHL

F20-NHL

Fig. 8. Compressive strength and strength variation before and after mortars were immersed in Na2SO4 solution.

4.0 NHL S10-NHL S20-NHL F10-NHL F20-NHL

Heat release rate(J/g·h)

3.5 3.0 2.5 2.0

4.0

3.0 2.5 2.0 1.5 1.0 0.5

1.5

(b) 250

60

225

50

NHL S10-NHL S20-NHL F10-NHL F20-NHL

3.5

Heat release rate(J/g·h)

(a)

0.0

0

4

8

12

16

20

24

Hydration time(h)

1.0

200

Total heat release(J/g)

14

Strength variation percentages (% )

Compressive strength of mortars before and after sodium sulfate (MPa)

100

Compressive strength before sodium sulfate Compressive strength after sodium sulfate Compressive strength variation percentages

16

exothermic peak. The second exothermic peak in NHL pastes represented the hydration of C2S to form C-S-H, but the growth of exothermic rate was lower and the duration of this stage was short relatively, This was due to the hydration rate of unit amount of C2S and total heat release all were lowest in the four mineral phases of Portland cement (C3S, C2S, C3A and C4AF) [31]. The C-S(A)-H was generated by hydration reaction of C2S and pozzolanic reaction of slag powder in S-NHL pastes and released a great deal of heat quantity [39], The hydration heat release rate of the paste was greatly increased at this stage (It’s almost three times better than the NHL paste), and the duration of this stage was longer, the results show that the slag powder to substitute partial NHL could promote the hydration reaction of S-NHL pastes largely. The peak shape of the second exothermic peak of F-NHL pastes were similar to NHL paste, it shows that this stage taking the hydration reaction of C2S as a leading, while the incorporation of silica fume had lesser impact on the hydration reaction. After 20 h, the third exothermic peak appeared in all NHL based pastes (except S10NHL paste), the hydration of C2S was accompanied by pozzolanic reaction, and then the hydration rate gradually decreased and tend to stabilize. After the third exothermic peak of NHL paste, the heat release rate decreased gradually and tends to zero, whereas the hydration heat release rate of S-NHL and F-NHL pastes also maintained a certain rate, thereinto, S20-NHL paste had a higher exothermic rate for a long time, and the hydration exothermic rate of F20-NHL paste had been maintained at 0.5 J/(gh), it was indicated that the pozzolanic reaction was still carried out in the later hydration stage of F-NHL pastes. From the total hydration heat release, show this tendency: FNHL > S-NHL > NHL before 12 h, then with the increase of hydration heat release rate of S-NHL pastes, the total heat release was increased gradually, in this period, the tendency was: S-NHL > FNHL > NHL, and had continuing until about 150 h. Due to the pozzolanic reaction of F20-NHL paste was continuing in the late stage, total heat release of F20-NHL paste exceeded the S10-NHL paste, and the total heat release of S20-NHL paste was much larger than other NHL based pastes. In addition, the total hydration heat release of NHL based pastes were increased with the increase of pozzolanic materials dosage, and the increasing range was proportional to the dosage of pozzolanic materials. In general, the hydration heat release rate and total heat release of S-NHL pastes were increased greatly by the use of slag powder; although the impact of silica fume on the early hydration rate of F-NHL pastes were minor, but the hydration rate was remained at a certain level in the later stage and the total hydration heat release of 7 days was higher than NHL paste.

Total heat release(J/g)

8

175 150

NHL S10-NHL S20-NHL F10-NHL F20-NHL

40

30

20

10

125 0 0

100

4

8

12

16

20

24

Hydration time(h)

75 50

0.5

25

0.0

NHL F10-NHL

0

0

20

40

60

80

100

Hydration time(h)

120

140

160

0

20

40

60

80

100

S10-NHL F20-NHL

120

Hydration time(h)

Fig. 9. (a) Hydration heat release rate and (b) Total heat release of NHL, S-NHL and F-NHL pastes with hydration time at 25°C.

S20-NHL

140

160

D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

3.5. TG-DTA analysis of hardened NHL based pastes Fig. 10 shows the thermal analysis of NHL2 at 28 days, where it can be seen that the DTA curve of the products of hardened pastes have four endothermic peaks in different temperature ranges. It can be seen from the TG and DTA curves that the products of paste underwent five distinct mass loss (ML) processes [32–34], as follows: the ML below T0 is due to the evaporation of free water, dehydration of hydrate compound at T0 to T1, the ML of T1  T2 is caused by dehydration of magnesium hydroxide, dehydration of Ca(OH)2 at T2 to T3 and decomposition of CaCO3 at T3 to T4. To evaluated the change in the hardening process of the pastes with the curing ages, according to the ML of each stage by TG-DTA analysis, the content of Ca(OH)2 and CaCO3 by carbonization in mortars at different curing ages were calculated respectively according to Eqs. (11) and (12):

CHR ¼ MLðT 2 T 3 Þ  k1

ð11Þ

CCCarb ¼ MLðT 3 T 4 Þ  k2  CC RM

ð12Þ

k1 ¼

MW CaðOHÞ MW H

2O

2

(MWCa(OH)2, MWH2O — Relative molecular mass of Ca

(OH)2 and H2O, respectively, 74 and 18); k2 ¼

MW CaCO

3

MW CO

2

(MWCaCO3,

MWCO2 – Relative molecular mass of CaCO3 and CO2, respectively, 100 and 44); where ML(T2  T3) is mass loss in the TG curves (%) between T2 to T3, ML(T3  T4) is mass loss in the TG curves (%) between T3 to T4, CHR is the Ca(OH)2 content in mortar at different curing ages (%), CCcarb refers to the production of CaCO3 by the carbonation, CCRM is the content of CaCO3 in raw materials.

Fig. 10. TG-DTA curve of NHL2 at curing age of 28 days.

9

The content of Ca(OH)2 in the NHL based pastes cured at different ages (14, 28 and 90 days) is shown in Fig. 11(a). Fig. 11(b) express the change of CaCO3 content by carbonization. NHL paste contained the most Ca(OH)2 at the same curing period and the carbonization degree was highest in the later period (after 28 days), the Ca(OH)2 content of pastes were decreased with the increasing of slag powder and silica fume content, and it had a significant decrease by pozzolanic materials to substitute partial NHL, while the CaCO3 content of pastes increased with the extension of the curing period, it also can be seen that the carbonization degree was lower in the early period (before 28 days) and the carbonization mainly occurred at the later curing period. With the increasing of slag powder and silica fume content, the Ca(OH)2 content of paste decreased at the same curing period, this was owing to the active SiO2 or/and Al2O3 of slag powder or silica fume occurred pozzolanic reaction with Ca(OH)2 in the water and formed hydration products such as C-S(A)-H and others, the process consumed massive Ca(OH)2, and the carbonation reaction also consumed partial Ca(OH)2. Moon et al. [16] researched that effect of blast furnace slag on the hydration properties in natural hydraulic lime, and by the test of DSC, The endothermic peaks by dehydration of hydrates and decarbonation of CaCO3 were increased by the latent hydraulic reaction and the carbonation reaction of Ca(OH)2 as time passes, meanwhile, the dehydroxylation of Ca(OH)2 decreased with an increase of hydration time, this is consistent with the results by TG-DTA of this paper. Otherwise, according to the work of Xu et al. [24], Content of Ca(OH)2 in diatomite-NHL and fly ash-NHL mortars prepared with diatomite and fly ash addition decreased with curing ages and this phenomenon was attributed to the comprehensive effect of hydration, carbonation and pozzolanic reaction, diatomite and fly ash also as pozzolanic materials, there are similar results with this research. Combined with Section 3.2, according to the development process of mechanical properties of all pastes, at curing period of 14 days, the Ca(OH)2 content of S-NHL pastes were higher F-NHL pastes under the same dosage of slag powder and silica fume, and the CaCO3 content of S-NHL pastes were lower than F-NHL pastes. The carbonization degree of each pastes was lower at 28 days, and at curing period of 90 days, the Ca(OH)2 content of S-NHL pastes were lower F-NHL pastes under the same dosage of slag powder and silica fume, and the CaCO3 content of S-NHL pastes were higher than F-NHL pastes, the results indicated the early pozzolanic reaction of S-NHL pastes were slow relatively, whereas F-NHL pastes were rapid relatively. Generally speaking, the early strength development of pastes was mainly affected the formation of C-S(A)-H by the hydration reaction of C2S phase in NHL and pozzolanic reaction of amorphous Si-Al phases in

Fig. 11. (a) The content of Ca(OH)2 and (b) CaCO3 by carbonization reaction in lime based mortars at different curing ages.

D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

3.6. Micro-morphologies of hardened NHL based pastes The micro-morphologies of NHL, S-NHL and F-NHL pastes at curing period of 90 days are shown in Fig. 12. It can be observed that the silicate mineral phase occurred hydration reaction in the NHL pastes to produce partial needle-shaped and amorphous calcium silicate hydrate (C-S-H) at 90 days of hardening, which was filled in the cavity. Meanwhile, major cubic CaCO3 crystal was generated in paste, and there were more pores, loose structure and larger porosity in the morphology of the paste. The hydration products of S10-NHL pastes mainly existed in the form of fibrous and network state at 90 days, and the hydration products intertwined each other and wrapped on the surface of Ca(OH)2. The hydration and pozzolanic reaction of S20-NHL pastes generated many fibrous and network hydration products (C-S(A)-H) with larger size, and the C-S(A)-H coated on the surface of Ca(OH)2 closely. A large number of cubic CaCO3 crystal was formed by carbonation reaction that was visible clearly, which intertwined with the C-S (A)-H and the unreacted mineral phases and filled in the pores of paste, a relatively compact structure was formed. Ca(OH)2 reacted with active SiO2 to form a spot of fine bar and more network C-S-H wrapped in the surface of Ca(OH)2 in F10-NHL paste, the cubic CaCO3 crystal was formed by carbonation of Ca(OH)2 were intertwined with the network C-S-H and wrapped on the surface of Ca(OH)2, which filled the pore structure and a compact microstructure was formed. The morphology of F20-NHL paste was similar to F10-NHL paste at 90 days, the morphology of C-S-H was mainly in the shape of fine rod and network state, and the unhydrated spherical silica fume particles existed in the form of single or cluster can be observed. In comparison, the hardening products and their existential forms of NHL, S-NHL and F-NHL pastes have different types due to different mineral phases, and there have the different microstructure, it is also observed that the structure compactness of S-NHL and F-NHL pastes are higher than NHL paste.

3.7. Evaluation of pozzolanic effect The relative compressive strength (RCS) and pozzolanic indexes P of S-NHL and F-NHL mortars after 14, 28, 90 and 180 days of curing ages are shown in Fig. 13. RCS is defined as the ratio of compressive strength of S-NHL/F-NHL mortars to NHL2 mortar, here, the relative compressive strength of NHL mortar is 1. The pozzolanic index P can effectively explain the influence of pozzolanic reaction caused by pozzolanic materials on the mechanical properties of mortars. Fig. 12 shows that there is a positive correlation obviously between the RCS of mortars and the pozzolanic indexes, the higher pozzolanic indexes P corresponding to the higher RCS, and the P of mortars increase greatly with the increasing of slag powder or silica fume content. Meanwhile, the pozzolanic indexes P of S-NHL mortars enhance with the prolonging of curing period, whereas the P of F-NHL mortars mixing silica fume reached its maximum value at 28 days of curing period, since then, the P has decreased. In addition, the pozzolanic index P of S-NHL mortars were low relatively at 14 days, while the P of F-NHL mortars were highest at 28 days. According to these correlativity, the pozzolanic

4.5 4.0 3.5

14d RCS 28d RCS 90d RCS 180d RCS

80

14d 28d 90d 180d

75 70

3.0 2.5

65

2.0 60 1.5

Pozzolanic Index,P(%)

pozzolanic materials, the later strength growth mainly derived from the carbonation process to form CaCO3 and accompanied by a degree of hydration reaction, but carbonation had little effect on strength development and the strength growth was slower.

Relative compressive strength

10

55

1.0 0.5

50

0.0 S10-NHL

S20-NHL

F10-NHL

F20-NHL

Fig. 13. Correlation between relative compressive strength and pozzolanic index P of different mortars at each curing period.

Fig. 12. SEM images of all kinds of NHL based pastes at the curing period of 90 days.

D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

reaction between slag powder and Ca(OH)2 can be extended to the later curing period, while the pozzolanic reaction between silica fume and Ca(OH)2 was occurred during the early curing period. Before the curing period of 28 days, the pozzolanic effect P of silica fume was higher than slag powder, and there had an opposite result in later curing period. Slag powder was more effective than silica fume in improving the compressive strength of mortars. 4. Conclusions Based on the above results, the following conclusions can be drawn: (1) For the macro properties of all NHL based mortars, the fluidity of F10-NHL and F20-NHL fresh mortars were decreased by 8.3% and 12.25% compared with the NHL fresh mortar; the use of silica fume had a greater influence on the water absorption of NHL based mortars compared with slag powder. Silica fume had a more positive effect on the early compressive strength of NHL based mortars, while slag powder had a more significant improvement on the long-term compressive strength of NHL based mortar, the CS of S20-NHL and F20-NHL mortars raised 217% and 227% compared with NHL mortar at 28 days respectively, and severally raised 235% and 196% at 180 days. (2) Pozzolanic materials to substitute partial NHL can improve the acid resistance and sulfate resistance of NHL based mortar effectively, compared with slag powder, silica fume had obvious improvement to sulfate resistance of mortars. (3) With the addition of slag powder or silica fume, the pozzolanic reaction occurred in NHL based mortars and more C-S(A)-H was formed, thereinto, slag powder can greatly improve the hydration reaction of S-NHL mortars, and silica fume to substitute partial NHL can make the hydration reaction of F-NHL mortars maintaining a higher rate in the later curing period. Combined with the strength growth process of all mortars, the early strength development of mortars were mainly affected the formation of C-S(A)-H by the hydration reaction of C2S phase in NHL and pozzolanic reaction of amorphous Si-Al phases in pozzolanic materials, the later strength growth mainly derived from the carbonation process to form CaCO3 and accompanied by a degree of hydration and pozzolanic reaction, but carbonation had little effect on strength development and the strength growth was slower. (4) The hardening products and their existential forms of NHL, S-NHL and F-NHL mortars have different types due to different mineral phases, and there have different microstructures, it is also observed that the structure compactness of S-NHL and F-NHL mortars are higher than NHL mortar. The pozzolanic reaction between slag powder and Ca(OH)2 can be extended to the later curing period (after 28 days), while the pozzolanic reaction between silica fume and Ca(OH)2 was occurred during the early curing period (before 28 days). The pozzolanic effect of silica fume is higher than slag powder before 28 days, and slag powder is higher than silica fume after 28 days, besides, slag powder has better effect for improving the compressive strength of NHL based mortars compared with silica fume. CRediT authorship contribution statement Dajiang Zhang: Conceptualization, Methodology, Investigation, Writing - original draft. Jihui Zhao: Writing - review & editing, Validation, Formal analysis, Visualization. Dongmin Wang:

11

Writing - review & editing, Validation, Formal analysis, Visualization. Yiren Wang: Writing - review & editing. Xiangdong Ma: Writing - review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (No. 5157020997); the National Key Research and Development Program of China (No. 2017YFC0505904); the Beijing Municipal Natural Science Foundation, China (No. 2184118); and the National Key Research and Development Project (No. 2017YFC0703200). References [1] J. Lanas, J.L.P. Bernal, M.A. Bello, J.I.A. Galindo, Mechanical properties of natural hydraulic lime-based mortars, Cem. Concr. Res. 34 (2004) 2191–2201. [2] K. Callebaut, J. Elsen, K.V. Balen, W. Viaene, Nineteenth century hydraulic restoration mortars in the saint michael’s church (leuven, belgium): natural hydraulic lime or cement?, Cem. Concr. Res. 31 (2001) 397–403. [3] P. Maravelaki-Kalaitzaki, A. Bakolas, I. Karatasios, V. Kilikoglou, Hydraulic lime mortars for the restoration of historic masonry in Crete, Cem. Concr. Res. 35 (2005) 1577–1586. [4] C. Sabbioni, G. Zappia, C. Riontino, M.T. Blanco-Varela, J. Aguilera, F. Puertas, K. Van Balen, E.E. Toumbakari, Atmospheric deterioration of ancient and modern hydraulic mortars, Atmos. Environ. 35 (2001) 539–548. [5] A. El-Turki, R.J. Ball, M.A. Carter, M.A. Wilson, C. Ince, G.C. Allen, Effect of dewatering on the strength of lime and cement mortars, J. Am. Ceram. Soc. 93 (2010) 2074–2081. [6] A. El-Turki, R.J. Ball, S. Holmes, W.J. Allen, G.C. Allen, Environmental cycling and laboratory testing to evaluate the significance of moisture control for lime mortars, Constr. Build. Mater. 24 (2010) 1392–1397. [7] C. Sabbioni, A. Bonazza, G. Zappia, Damage on hydraulic mortars: the Venice Arsenal, J. Cult. Herit. 3 (2002) 83–88. [8] B.A. Silva, A.P.F. Pinto, A. Gomes, Natural hydraulic lime versus cement for blended lime mortars for restoration works, Constr. Build. Mater. 94 (2015) 346–360. [9] A. Bras, F.M.A. Henriques, M.T. Cidade, Effect of environmental temperature and fly ash addition in hydraulic lime grout behaviour, Constr. Build. Mater. 24 (2010) 1511–1517. [10] J. Grilo, P. Faria, R. Veiga, A.S. Silva, V. Silva, A. Velosa, New natural hydraulic lime mortars-physical and microstructural properties in different curing conditions, Constr. Build. Mater. 54 (2014) 378–384. [11] C.J. Tsai, R. Huang, W.T. Lin, H.N. Wang, Mechanical and cementitious characteristics of ground granulated blast furnace slag and basic oxygen furnace slag blended mortar, Mater. Des. 60 (2014) 267–273. [12] J.A. Bogas, R. Nogueira, N.G. Almeida, Influence of mineral additions and different compositional parameters on the shrinkage of structural expanded clay lightweight concrete, Mater. Des. 56 (2014) 1039–1048. [13] K. Gäbel, A.M. Tillman, Simulating operational alternatives for future cement production, J. Clean. Prod. 13 (2005) 1246–1257. [14] N. Shanahan, A. Markandeya, A. Elnihum, Y.P. Stetsko, A. Zayed, Multitechnique investigation of metakaolin and slag blended portland cement pastes, Appl. Clay Sci. 132 (2016) 449–459. [15] E. Gruyaert, N. Robeyst, N.D. Belie, Study of the hydration of Portland cement blended with blast-furnace slag by calorimetry and thermogravimetry, J. Therm. Anal. Calorim. 102 (2010) 941–951. [16] K.Y. Moon, J.S. Choa, M.K. Choi, K.H. Cho, J.W. Ahn, C.W. Hong, S.C. Ur, Effect of blast furnace slag on the hydration properties in natural hydraulic lime, J. Ceram. Process. Res. 17 (2016) 122–128. [17] H. Zhao, W. Sun, X.M. Wu, B. Gao, The properties of the self-compacting concrete with fly ash and ground granulated blast furnace slag mineral admixtures, J. Clean. Prod. 95 (2015) 66–74. [18] P. Yan, B. Zhang, Mechanical properties of high strength concrete prepared with different densities of silica fume, J. Chin. Ceram. Soc. 44 (2016) 196–201 (in chinese). [19] L.G. Baltazar, F.M.A. Henriques, F. Jorne, M.T. Cidade, Combined effect of superplasticizer, silica fume and temperature in the performance of natural hydraulic lime grouts, Constr. Build. Mater. 50 (2014) 584–597. [20] R. Cˇerny´, A. Kunca, V. Tydlitát, J. Drchalová, P. Rovnaníková, Effect of pozzolanic admixtures on mechanical, thermal and hygric properties of lime plasters, Constr. Build. Mater. 20 (2006) 849–857.

12

D. Zhang et al. / Construction and Building Materials 244 (2020) 118360

[21] P. Dybeł, K. Furtak, Influence of silica fume content on the quality of bond conditions in high-performance concrete specimens, Arch. Civ. Mech. Eng. 17 (2017) 795–805. [22] J. Xie, C. Fang, Z. Lu, Z. Li, L. Li, Effects of the addition of silica fume and rubber particles on the compressive behaviour of recycled aggregate concrete with steel fibres, J. Clean. Prod. 197 (2018) 656–667. [23] W. Zhang, H. Ba, Effect of ground granulated blast-furnace slag (GGBFS) and silica fume (SF) on chloride migration through concrete subjected to repeated loading, Sci. China. Technol. Sci. 55 (2012) 3102–3108. [24] S. Xu, J. Wang, Q. Jiang, S. Zhang, Study of natural hydraulic lime-based mortars prepared with masonry waste powder as aggregate and diatomite/fly ash as mineral admixtures, J. Clean. Prod. 119 (2016) 118–127. [25] C. Borges, A.S. Silva, R. Veiga, Durability of ancient lime mortars in humid environment, Constr. Build. Mater. 66 (2014) 606–620. [26] P.F.G. Banfill, E.M. Szadurski, A.M. Forster, Deterioration of natural hydraulic lime mortars, II: Effects of chemically accelerated leaching on physical and mechanical properties of carbonated materials, Constr. Build. Mater. 111 (2016) 182–190. [27] L. Li, L. Zhao, J. Wang, Z. Li, The study of physical and mechanical properties of two traditional silicate materials in ancient Chinese architecture, Chin. J. Rock Mech. Eng. 30 (2011) 2120–2127 (in Chinese). [28] V. Pavlík, M. Uzˇáková, Effect of curing conditions on the properties of lime, lime-metakaolin and lime-zeolite mortars, Constr. Build. Mater. 102 (2016) 14–25. [29] A. Izaguirre, J. Lanas, J.I. Álvarez, Ageing of lime mortars with admixtures: durability and strength assessment, Cem. Concr. Res. 40 (2010) 1081–1095. [30] L. Yu, H. Ou, L.L. Lee, Investigation on pozzolanic effect of perlite powder in concrete, Cem. Concr. Res. 33 (2003) 73–76. [31] Z. Lin, Inorganic Matalloid Materials Technics, third ed., Wuhan University of Technology Press, Wuhan, 2008 (in chinese). [32] L.P. Esteves, On the hydration of water-entrained cement-silica systems: combined SEM, XRD and thermal analysis in cement pastes, Thermochim. Acta 518 (2011) 27–35. [33] V. Lilkov, O. Petrov, Y. Tzvetanova, P. Savov, Mössbauer, DTA and XRD study of Portland cement blended with fly ash and silica fume, Constr. Build. Mater. 29 (2012) 33–41.

[34] H.F.W. Taylor, Cement Chemistry, second ed., Thomas Telford, 1997. [35] R. Veiga, Air lime mortars: what else do we need to know to apply them in conservation and rehabilitation interventions? A review, Constr. Build. Mater. 157 (2017) 132–140. [36] Y. Xu, L. Zhang, Y. Lu, Influence of fly ash, slag and silica fume on cement mortar fluidity and early strength, Concrete 9 (2005) 39–41 (in Chinese). [37] N. Feng, High-performance Concrete Structure, China Machine Press, 2004 (in Chinese). [38] S. Xu, Q. Ma, J. Wang, L. Wang, Grouting performance improvement for natural hydraulic lime-based grout via incorporating silica fume and silicon-acrylic latex, Constr. Build. Mater. 186 (2018) 652–659. [39] W. Chen, H.J.H. Brouwers, The hydration of slag, part 2: reaction models for blended cement, J. Mater. Sci. 42 (2007) 444–464. [40] D. Deng, Z. Liu, Y. Liu, Research progress on theory of ‘‘sulfate salt weathering on concrete”, J. Chin. Ceram. Soc. 40 (2012) 175–185 (in Chinese). [41] EN BS 459-1, Building Lime – Part 1: Definitions, Specifications and Conformity Criteria, 2010. [42] EN BS 459-2, Building Lime – Part 2: Test Methods, 2010. [43] EN BS 197-1, Cement-Part 1: Composition, Specifications and Conformity Criteria for Common Cements, 2000. [44] GB/T 17671-1999, Method of Testing Cements – Determination of Strength (ISO), 1999 (Chinese Standard). [45] JC/T 681-2005, Mixer for Mixing Mortars, 2005 (Chinese Standard). [46] GB/T 2419-2005, Test Method for Fluidity of Cement Mortar, 2005 (Chinese Standard). [47] JGJ/T 70-2009, Standard for Test Method of Basic Properties of Construction Mortar, 2009 (Chinese Standard). [48] K.Y. Moon, M.K. Choi, K.H. Cho, J.S. Cho, J.W. Ahn, C.W. Hong, Effect of gypsum on hydration properties of natural hydraulic lime, J. Korean Inst. Resour. Recycl. 24 (2015) 12–20. [49] X. Zhang, G. Zhang, D. Sun, K. Liu, Progress of the mechanism of sulfate attack on cement-based materials, Mater. Rev. 32 (2018) 1174–1180 (in Chinese). [50] EN BS 1015-11, Methods of Test for Mortar for Masonry-Part 11: Determination of Flexural and Compressive Strength of Hardened Mortar, 1999.