The molecular structures and the application properties of sulfonated acetone-formaldehyde superplasticizers at different synthetic methods

Construction and Building Materials 241 (2020) 118051

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The molecular structures and the application properties of sulfonated acetone-formaldehyde superplasticizers at different synthetic methods Hui Zhao ⇑, Ming Deng, Mingshu Tang College of Materials Science and Engineering, Nanjing University of Technology, 210004 Nanjing, China

h i g h l i g h t s  AOH, ACH2, AC@O, ASO3 groups are bonded in the molecule of SAF SP.  SAF-1 SP has higher Mn, Mw, PDI, sulfonic group content than SAF-2 SP.  SAF-1 SP has larger water-reducing ratio in the concrete than SAF-2 SP.  SAF-1 SP series concrete exhibit better fresh and mechanical properties.  Using sodium pyrosulfite at four-step is an effective method to prepare SAF SP.

a r t i c l e

i n f o

Article history: Received 19 June 2019 Received in revised form 24 December 2019 Accepted 2 January 2020

Keywords: Sulfonated acetone-formaldehyde Superplasticizer Synthetic method Molecular structure Application properties Concrete

a b s t r a c t Nowadays, Superplasticizers (SPs) are the basic component to produce the concrete. In this study, the water-soluble sulfonated acetone-formaldehyde (SAF) SP was prepared at different synthetic methods (SAF-1, SAF-2). The molecular structures and the application behaviors of SAF-1, SAF-2 SPs in the concrete were evaluated. The molecules of SAF-1, SAF-2 SPs have the same AOH, ACH2, AC@O, ASO3 groups. However, SAF-1 SP has the larger weight-average molecular weight (Mn), the number-average molecular weight (Mw), the polydispersity index (PDI) and the higher sulfonic group content than SAF-2 SP. The larger water-reducing ratio, the better fluidity preservation, the longer setting times, the larger bleeding water rate, wet density and mechanical behaviors of the concrete than those with SAF-2 SP can be found in the SAF-1 SP-blended concrete mixtures. The differences in the air content of the SAF-1, SAF-2 SPs series concrete are insignificant. Therefore, it is an effective method to prepare SAF SP using sodium pyrosulfite as sulfonating agent at four-step processes. Ó 2020 Elsevier Ltd. All rights reserved.

1. Introduction With the progress in the construction industry technology, chemical admixtures had become the basic component to prepare the concrete materials. In Japan, the commercial concrete products almost fully use chemical admixtures. Each year, the concrete materials with chemical admixtures account for about 50 % of the total amounts of the concrete in United State. Superplasticizers (SPs) are the most common of chemical admixtures used in the concrete industry, which exhibit good dispersing ability for the cement particle and substantially reduce water content in the concrete [1]. Because of the deep understood in the benefit of SPs, SPs as an indispensible part in the concrete materials had been widely applied in the large-scale buildings, roads, bridges, dams and

⇑ Corresponding author. E-mail address: [email protected] (H. Zhao). https://doi.org/10.1016/j.conbuildmat.2020.118051 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved.

marine structural engineering. The demand for SPs is everincreasing around the world [2]. Nowadays, the main types of SPs used in the concrete are modified lignosulphonate (MLS) SP, naphthalene sulfonate formaldehyde (NSF) SP, melamine sulfonate formaldehyde (MSF) SP and polycarboxylate (PCA) SP with the linear backbone chain and the comb-like side chain [3,4]. MLS SP has the poor water reduction rate, and needs to the combining utilization with the other SPs to prepare the concrete. Moreover, the presence of NSF, MSF SPs in the concrete improves the initial fluidity of the fresh concrete. However, the high amount of NSF, MSF SPs introduced to the concrete increase the slump loss of the fresh mixed concrete [5]. Also, PCA SP is sensitive to the chemical compositions of cement and easily interacts with clay particle in aggregates, which affects the dispersing ability of PCA SP in the concrete mixture [6]. Therefore, the new type of SP with high dispersing ability and better dispersing stability, compatibility with raw materials needs to develop for the production of the concrete materials.

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H. Zhao et al. / Construction and Building Materials 241 (2020) 118051

Between 1980 and 1990 year, the water-soluble sulfonated acetone-formaldehyde (SAF) resin with a high water-reduction percentage and low slump loss rate was first developed in China as SP. SAF SP had attracted more and more attention around the world [7]. SAF SP was prepared by the reactions among sulfonating agent, formaldehyde and acetone. The molecule of SAF SP has nonconjugated linear aliphatic chains with hydroxyl group (AOH) and sulfonic group (ASO3) [8]. The previous studies had shown [9,10] that the adsorption of SAF SP on the surface of the cement particle produces a large electrostatic repulsive force between the cement particles, which causes the improvement on the fluidity and the mechanical behaviors of the concrete. More SAF SP incorporating into the concrete were beneficial to prepare the concrete materials with high strength and more durable. The research results made by Lou et al. [11] showed that SAF SP with the high molecular weight exhibits a large adsorption amount, a high zeta potential absolute and a thick adsorbed film on the cement particle surface, which induces better dispersity for the cement particle. Pei et al. [12] reported that the optimum conditions of preparing SAF SP are the molar ratio of formaldehyde-anhydrous sodium sulfiteacetone for 2.0:0.6:1.0. The low temperature condensation and high temperature condensation were kept at 60–65 °C for 1 h and at 85 °C for 4 h. SAF SP synthesized under the optimum reaction conditions had the better dispersion ability for the cement particle. Up to now, a number of the extensive literatures proved that the dosage, the molecular weight, and the synthetic condition of SAF SP affect the dispersing behaviors of SAF SP in the concrete. However, few studies focus on the influence of the synthetic method on the molecular structure and the application properties of SAF SP in the concrete. Therefore, the further investigate needs to carry out in these aspects. In this study, the sulfonated acetone-formaldehyde (SAF) SP was produced at different methods (SAF-1 SP, SAF-2 SP). The functional group, the molecular weight and the sulfonic group content in the molecules of SAF-1, SAF-2 SPs were examined. Based on the above investigations, SAF-1, SAF-2 SPs at different dosages, ranging from 0% to 0.72%, were introduced to the concrete. The application properties of SAF-1, SAF-2 SPs in the concrete, i.e. the water-reducing percentage, the fluidity preservation, the air content, the bleeding water rate, the setting times, the wet density, the compressive strength, the flexural strength, the ultrasonic pulse velocity, were evaluated. The optimum synthetic method of SAF SP to prepare the concrete materials was presented.

2. Experimental 2.1. Synthesis of SAF SP 2.1.1. SAF-1 Sp SAF-1 SP was synthesized by the reactions among sodium pyrosulfite (SPS), acetone (A), formaldehyde of 37% concentration (F). First, SPS (151.41 g) and F (35.11 g) were stirred until the mixture solution became clear, and cooled to room temperature. After that, A (56.08 g) and 40% sodium hydroxide (NaOH) solution (31.05 g) were fed into the reactor. The reactive system was neutralized to pH value for 11–12. Then, the mixture solutions of SPS and F were fed into the reactor for 3 h, and the temperature of the reaction system was controlled below 50 °C. Finally, the temperature of the solution was raised to 85–90 °C for another 4 h. The product of the reaction was diluted with 97.71 g water. After a certain time of cooling, the solution of SAF-1 SP with the solid content of 39–40 % and pH value of 11.63 was obtained.

2.1.2. SAF-2 Sp SAF-2 SP was prepared from anhydrous sodium sulfite (ASS), acetone (A), formaldehyde of 37% concentration (F) and water (W). The molar ratio of ASS: A: F: W was constant at 0.7:1:2: 1.56. First, ASS was dissolved into water. Then, the mixture was heated up to 50 °C, A was added into the mixture solution stirring for 1 h. After that, F was dropped into the reactor. During the feeding course, the solution was kept at the temperature of 65 °C for 1 h. Finally, the reaction was completed after continuously stirring at 90 °C for another 4 h. The product of SAF-2 SP cooled to room temperature had the concentration of 32 % and pH value of 10.5– 11.0. 2.2. Characterization of SAF SP Fourier transform infrared (FT-IR) analysis was measured to determine the functional groups of synthesized SAF SP, using NEXUS 670 FT-IR instrument (Nicolet Corporation, USA). The solution of SAF SP was dried in an oven at 60 °C for 24 h. Then, the dried SAF SP was ground to powder and mixed with potassium bromide. Finally, the mixture was compacted into a disk. FT-IR spectrum of SAF SP sample was recorded at the wave number range of 4000– 400 cm 1. The molecular parameter of synthesized SAF SP was evaluated by the weight-average molecular weight (Mw), the numberaverage molecular weight (Mn), the polydispersity index (PDI: Mw/Mn). Gel Permeation Chromatograph (GPC) apparatus equipped with Ultrahydrogel columns of 120, 250, 500 (Waters 1515, Waters Corp, USA) was employed to determine Mw, Mn of SAF SP. In the test, 0.10 mol/L sodium chloride solution (pH of the solution adjusted to 12 with NaOH) as carrying phase at a flow rate of 0.5 mL/min, the mono-dispersive sodium polyethylene sulfonate as the standard phase of calibration. The potentiometric titration method was introduced to test the sulfonic group content in the molecule of SAF SP. Before the measurement of titration, the sample was ion-exchanged to remove salt and other impure substances. Then, the sample was turn into the corresponding acids. Finally, the sulfonic group content was obtained by automatic potentiometric titrator (905 Titrando, Metrohm Corporation, Switzerland). 2.3. Application properties of SAF SP in the concrete 2.3.1. Raw materials ASTM Type I Portland cement (PC), meeting the specification of ASTM C 150-07 [13], was used as the binder materials. The strength class of PC is 52.5. Table 1 gives the oxide compositions, the phase compositions and the physical properties of cement. SAF SP was prepared at different synthetic methods (SAF-1, SAF2). The chemical structure of the molecule of synthesizing SAF SP is given in Fig. 1. The properties of SAF-1, SAF-2 SPs are shown in Table 2. Natural river sand fine aggregate (less than 5.00 mm) was purchased from China. River sand fine aggregate had the oven-dry (OD) density, the saturated surface dry (SSD) density and the water absorption for 2580 kg/m3, 2620 kg/m3, 0.80 %. Natural crushed stones with two continuous gradations (sizes of 5–20 mm, 20–40 mm) were employed as coarse aggregate. The OD, SSD and water absorption of 5–20 mm, 20–40 mm coarse aggregates were 2632 kg/m3,2675 kg/m3,1.20% and 2618 kg/m3, 2659 kg/m3, 1.06 %. The particle grades of fine aggregate and coarse aggregates are given in Fig. 2. 2.3.2. Mixture proportions In this study, the concrete mixture was designed with a constant weight proportion of cement: fine aggregate: total coarse aggregates for 1/2.16/3.54. The content of cement was kept at

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H. Zhao et al. / Construction and Building Materials 241 (2020) 118051 Table 1 The oxide compositions, the phase compositions and the physical properties of cement. Oxide compositions (%)

SiO2 19.4

Al2O3 5.4

CaO 67.6

Phase compositions (%)

Fe2O3 2.2

MgO 0.1

SO3 3.8

K2O 0.5

Na2O 0.3

TiO2 0.215

C3S 77.8

C2S 16.9

C3A 10.5

Physical properties Specific gravity (g/cm3)

fineness (cm2/g)

3.16

3519

Fig. 1. The chemical structure of the molecule of SAF SP.

Table 2 The properties of SAF-1, SAF-2 SPs. Properties

SAF-1 SP

SAF-2 SP

Color Solid content (%) pH Alkali content (%) Sodium sulfate content (%) Chloride content (%)

Brown liquid 39–40 11.63 4.55 0.31 0.01

Brown liquid 31–33 10.89 3.26 0.22 0.01

concrete mixture continued to mix for another 300 sec. Before casting, the properties of the fresh concrete, i.e. the waterreducing percentage, the initial fluidity, the fluidity preservation, the air content, the bleeding water rate, the wet density, the setting times, were measured. After that, the fresh mixed concrete were poured into the moulds and vibrated for 120–180 sec. Finally, the compacted concrete mixtures were transferred to the room with a temperature of 20 °C for the first 24 h complying with GOST 10180 [14]. After 24 h, the concrete samples were demoulded and placed at the environment (the relative humidity of 90 ± 5%, the temperature of 20 °C) for 3, 7, 28 days. 2.3.4. Test methods 2.3.4.1. Water-reducing percentage. The water-reducing percentages of SAF SP in the concrete were conducted in accordance with Chinese standard GB/T 8076 method [15].The target slump values of all the series concrete samples were controlled at 90 ± 15 mm. The difference of the consumption of water between in the absence and in the presence of SAF SP was used to calculate the waterreducing percentages (WRP) of SAF SP in the concrete.

Fig. 2. The particle grades of river sand fine aggregate and crushed stone coarse aggregates.

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330 kg/m . A total of eleven concrete mixtures were prepared, including one reference concrete sample and ten concrete samples containing SAF-1, SAF-2 SPs of 0.16 %, 0.32 %, 0.48 %, 0.64 %, 0.72 %. The amounts of SAF-1, SAF-2 SPs mentioned are the weight percent of cement. At each dosage of SAF-1, SAF-2 SPs, mixing water was adjusted to achieve the proper initial slump value of 90 ± 15 mm. The mix proportions of all the concrete mixtures are presented in Table 3. 2.3.3. Sample preparation, curing conditions In the production process, the solid materials to prepare the concrete mixture were dry-mixed for 60 sec. Then, SAF SP premixed with water was introduced to the solid mixture, the

2.3.4.2. Fluidity and fluidity preservation. The fluidity of the fresh mixed concrete was examined by the slump test method based on BS EN 12350-2 [16]. After the fresh mixed concrete was poured into the slump cone and compacted, the slump cone was raised in a vertical direction. The difference between the height of the slump cone and the highest point of the sample was recorded as the initial slump of the concrete. The fluidity preservation was assessed by the slump change of the concrete at the time interval of 30, 60, 90, 120 min. Before each measurement, the sample was remixed for about 20 sec. 2.3.4.3. Air content. The air content value of the fresh mixed concrete was evaluated using the water column method in conformance with BS EN 12350-7 [17]. First, the concrete mixture was poured into the cylinder container. After that, the cover assembly in the container was clamped. Finally, water filled the apparatus, and the level of water in the standpipe was adjusted to zero. The air content of the concrete was reported. 2.3.4.4. Bleeding water rate. The bleeding water rate test of the concrete was identified based on BS EN 480-4 method [18]. The fresh concrete was poured into the cylindrical mould and stored for 1 h. Then, accumulated water on the surface of the concrete was removed at every 10 min during the first 40 min, then at 30 min intervals until the completion of the bleeding water. Removed water was weighed. The bleeding water rate (BWR) of the concrete

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Table 3 The mix proportions of the concrete. Sample

Dosage of SAF SP (%)

Water (kg/m3)

Cement (kg/m3)

Fine aggregate (kg/m3)

Control 0.16 % SAF-1 0.32 % SAF-1 0.48 % SAF-1 0.64 % SAF-1 0.72 % SAF-1 0.16 % SAF-2 0.32 % SAF-2 0.48 % SAF-2 0.64 % SAF-2 0.72 % SAF-2

0 0.16 0.32 0.48 0.64 0.72 0.16 0.32 0.48 0.64 0.72

200 186.4 171.6 163.6 155.8 148.2 187.4 172.4 164.8 157.6 150.8

330 330 330 330 330 330 330 330 330 330 330

710 710 710 710 710 710 710 710 710 710 710

SP SP SP SP SP SP SP SP SP SP

is equal to the weight percentage of removed water to the total weights of consumption water. 2.3.4.5. Setting times. The penetration resistance method was employed to evaluate the setting times of the concrete, based on BS EN 480-2 method [19]. During the test, the concrete mixture was passed through a sieve of 5 mm, and the fresh mortar was stored in the mould. At the regular intervals, the standard Vicat needle penetrates inside the mortar, the penetration depth was measured. The initial setting time of the mortar corresponds to the period when the distance between the needle and the bottom of the sample is 4.0 mm. The final setting time of the mortar was considered when the needle no longer penetrates the depth of 2.5 mm into the mortar sample. 2.3.4.6. Wet density. BS EN 12350-6 method [20] was introduced to test the wet density of the fresh mixed concrete. First, the fresh concrete was filled into the container and compacted. The fresh concrete in the container was weighted. The volume of the sample was calculated from its dimensions. The wet density (D) of the concrete is the weight of a unit volume of the fresh concrete expressed in kg/m3. 2.3.4.7. Compressive strength. At the curing periods of 3, 7, 28 days, three cube-shaped concrete samples (100 mm  100 mm  100 mm) were prepared for the uni-axial compressive strength test in accordance with BS EN 12390-3 method [21]. The compressive strength of the concrete mixture was assessed at a constant load rate of 0.3 N/mm2
s. 2.3.4.8. Flexural strength. After the concrete sample was stored in water for 3,7,28 days, a three-point flexural strength test was carried out under a central line load supported over a span of 450 mm complying with BS EN 12390-5 [22]. In the test, three prism samples of 100 mm  100 mm  400 mm were used to determine the flexural strength of the concrete at the constant load rate of 0.05 N/ mm2
s. 2.3.4.9. Ultrasonic pulse velocity (UPV). The ultrasonic pulse velocity (UPV) of the concrete was performed complying with ASTM C 59702 [23] on three 100 mm  100 mm  100 mm cube samples water-curing for 3, 7, 28, 90 days. 3. Results and discussion 3.1. Moleculal structures of SAF SP Table 4 presents that the absorption bands at 3512.87 cm 3441.73 cm 1, 3382.18 cm 1 and 3505.91 cm 1, 3389.7 cm

1

, ,

1

Coarse aggregates (kg/m3) 5–20 mm

20–40 mm

463 463 463 463 463 463 463 463 463 463 463

695 695 695 695 695 695 695 695 695 695 695

Initial slump (mm)

88 90 85 86 88 90 89 86 88 90 87

3378.67 cm 1 belong to the stretching vibration peak of hydroxyl (AOH) group. A strong characteristic absorption band correlating with the deform vibration of methylene (ACH2) group was observed at 2930.69 cm 1, 2855.45 cm 1 and 2928.87 cm 1, 2852.23 cm 1. The absorption peaks at 1703.98 cm 1, 1655.45 cm 1, 1607.92 cm 1 and 1697.61 cm 1, 1654.89 cm 1, 1608.15 cm 1 can be attributed to the stretching vibration of carbonyl (-C = O) group in the aliphatic molecular chain. The stretching vibration peak of sulfonic (-SO3) group was found at 1184.53 cm 1, 1044.80 cm 1 and 1182.51 cm 1, 1042.76 cm 1. The other typical absorption regions in FT-IR spectrum are at 764.36 cm 1, 617.82 cm 1 and 765.92 cm 1, 616.29 cm 1, which is the characteristic band of carbon-sulfur (-C-S) single bond [24– 27].The analysis of FT-IR spectrum proved that SAF-1, SAF-2 SPs are the aliphatic molecule with AOH, ACH2, AC@O, ASO3 functional groups. In case of synthesizing SAF SP at different methods, the wavenumber of AOH group in the molecule of SAF-2 SP shifts to low frequency for 5–10 cm 1, compared with the vibration peak of AOH group in the molecule of SAF-1 SP (3382.18 cm 1, 3512.87 cm 1). It indicated that the molecule of SAF-2 SP forms more intramolecular hydrogen bonds among the aliphatic hydroxyl group than SAF-1 SP. It is observed from Table 5 that Mw, Mn, PDI values of SAF-1, SAF-2 SPs are 36872 kDa, 34251 kDa, 1.743 and 21152 kDa, 20052 kDa, 1.708. SAF-1 SP has a relatively higher Mw, Mn and a wider weigh distribute range than that of SAF-2 SP. As shown in Table 5 that the molecules of SAF-1, SAF-2 SPs have the sulfonic group content for 3.52 mmol/g, 3.24 mmol/g. The sulfonic group content in the molecule of SAF-1 SP is 8.64% higher than that of SAF-2 SP. 3.2. Application properties of SAF SP in the concrete 3.2.1. Water-reducing percentage The water-reducing percentages of SAF SP at different dosages in the concrete were presented in Fig. 3. As expected, the incorporation of 0.16% SAF-1, SAF-2 SPs into the concrete reduces the water demand for 6.8%, 6.3%. The dosage of SAF SP changes from 0.16% to 0.32 %, 0.48 %, the water-reducing percentages of SAF-1, SAF-2 SPs in the concrete considerably enhance for 14.2 %, 19.2 % and 13.8 %, 18. 6 %, which had surpassed the value of 11 %, specified as Type F SPs, according to ASTM C 494 [28]. More than 0.48 % SAF SP was added into the concrete, the reduction in the water content of the concrete becomes very slowly, the saturation dosage of SAF SP in this condition is 0.48 %. The previously study [29] had shown the inclusion of SAF SP in the concrete increases the initial zeta potential value of the cement particle surface and lowers the inter-particle friction between the cement particles. Free water trapped on the flocculated cement particles was released, and the

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H. Zhao et al. / Construction and Building Materials 241 (2020) 118051 Table 4 FT-IR characteristic bands of SAF-1, SAF-2 SPs (cm

1

).

Sample

AOH

ACH2

AC@O

AS@O

ACAS

SAF-1 SP SAF-2 SP

3512.87, 3441.73, 3382.18 3505.91, 3389.7, 3378.67

2930.69, 2855.45 2928.87, 2852.23

1703.98,1655.45,1607.92 1697.61,1654.89,1608.15

1184.53, 1044.80 1182.51 1042.76

764.36, 617.82 765.92, 616.29

Table 5 The molecular weights, the polydispersity indexes and the sulfonic group contents of SAF-1, SAF-2 SPs. Sample

SAF-1 SP SAF-2 SP

Molecular weight (kDa) Weight-average molecular weight (Mw)

Number-average molecular weight (Mn)

36,872 34,251

21,152 20,052

Polydispersity index (PDI: Mw/Mn)

Sulfonic group content (mmol/g)

1.743 1.708

3.52 3.24

Fig. 3. The water reduction percentages of SAF-1, SAF-2 SPs in the concrete at different dosages.

water demand in the concrete mixture reduces. Moreover, at the same dosage, utilizing SAF-1 SP in the concrete has the higher water-reducing percentage than SAF-2 SP. It can be explained by this fact that the molecule of SAF-1 SP has more sulfonic group content than that of SAF-2 SP, which produces strong electrostatic repulsion force between the cement particles 3.2.2. Fluidity preservation The time-dependent change in the slump of the concrete with SAF-1, SAF-2 SPs at different dosages was investigated and shown in Fig. 4. At the same initial slump value of 90 ± 15 mm, the regardless of the dosage of SAF SP in the concrete, the slump value of the concrete reduces with the passage of time. A small amount of SAF SP (0.16 %) was introduced to the concrete mixture, the slump loss rates of the concrete with 0.16% SAF-1, SAF-2 SPs, after 2 h, change from 88.63%, in the concrete without SAF SP, to 83.33 %. 87.64 %. The futher increase in the amount of SAF SP from 0.16 % to 0.32 %. 0.48 %, the concrete mixtures with 0.32 %, 0.48 % SAF-1, SAF-2 SPs have the low slump flow loss rates (2 h) for 67.06 %, 62.79 % and 74.42 %, 72.73 %. The content of SAF SP in the concrete is greater than 0.48%, the notable low slump loss rates for 51.13 %, 46.6 7% and 62.22 %, 54.03 %, after 2 h, were observed in the concrete prepared by 0.64 %, 0.72 % SAF-1, SAF-2 SPs. The introduction of SAF SP to the concrete mixture improves the fluidity preservation of the concrete. It is because that the dispersing stability of SAF SP in the concrete origins from the electrostatic repulsive force between the cement particles, more SAF SP incorporating into the concrete compensate the lost of the electrostatic repulsive force between the

Fig. 4. The slump changes of the concrete incorporating SAF-1, SAF-2 SPs at different dosages with elapsed time.

cement particles with elapsed time, SAF SP can keep the better dispersing ability for the cement particle at a long time [30,31]. Besides, SAF-1 SP has the higher molecular weight and sulfonic group content than SAF-2 SP, which causes an increase in the density of electric charge and a high zeta potential absolute value on the cement particle surface [32].Therefore, the SAF-1 SP series concrete exhibit the better fluidity preservation than those with SAF-2 SP.

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3.2.3. Air content The air content test results of the SAF SP series concrete mixtures are summarized in Fig. 5. It is seen that, in case of the control concrete, the air content is 1.34%. The addition of 0.16%, 0.32% SAF1, SAF-2 SPs into the concrete exhibits the high air content for 1.46%, 1.57% and 1.47%, 1.56%. With the further increase in the amount of SAF SP from 0.32% to 0.48%, the notable large air content (1.82 % and 1.84 %) was obtained in the concrete samples with 0.48 % SAF-1, SAF-2 SPs. The amount of SAF SP in the concrete exceeds 0.48 %, the air content values of the concrete mixtures with 0.64 %, 0.72 % SAF-1, SAF-2 SPs have an increase very slowly for 2.16 %, 2.24 % and 2.17 %, 2.25 %. However, the air content had surpassed the limit value of 2 %, required by British Standards EN 934-2 [33]. Szwabowski and Łazniewska-Piekarczyk [34] think SAF SP adsorbed on the cement particle surface makes the agglomerated cement particle more disperse, and the air bubble in the fresh concrete can move freely. At the same dosage of SAF SP, the differences on the air content values of the concrete with SAF-1, SAF-2 SPs are no obvious. 3.2.4. Bleeding water rate Fig. 6 gives the bleeding water rates of the concrete samples with SAF SP at different dosages. It was found that the concrete with SAF-1, SAF-2 SPs of 0 %, 0.16 %, 0.32 %, 0.48 %, 0.64 %, 0.72 % have the bleeding water rate in the ranges of 1.77–8.08 %, 1.77%-

Fig. 6. The bleeding water rates of the concrete with SAF-1, SAF-2 SPs at different dosages.

7.59 %. The utilizing of 0.16 %, 0.32 % SAF-1, SAF-2 SPs in the concrete causes 27.68 %, 100.56 % and 21.47 %, 79.10 % higher bleeding water rate than the control concrete. The excessive use of SAF-1, SAF-2 SPs (higher than 0.32%) in the concrete mixture causes the increase rapidly in the bleeding water rate of the concrete. In all the SAF SP series concrete, the highest bleeding water rate can be recorded in the concrete containing 0.72 % SAF-1, SAF-2 SPs, which had exceeded the bleeding water rate value of 7 %. Kim et al. [35] explained the reason why the addition of SAF SP into the concrete increases the bleeding water rate of the concrete, their findings revealed that the molecule of SAF SP with -SO3 group exhibits the better dispersing ability for the cement particle, which increases the distance between the single cement particle, mixed water can easy to appear on the surface of the cement paste. In addition, the bleeding water rate of the concrete depends on the synthetic method of SAF SP. At the given content of SAF SP, SAF1 SP produces the stronger electrostatic repulsive force than SAF2 SP between the cement particles. The effectiveness of SAF-1 SP in enhancing the bleeding water rate of the concrete is more significant than SAF-2 SP.

Fig. 5. The air contents of the concrete with SAF-1, SAF-2 SPs at different dosages.

3.2.5. Setting times Fig. 7 illustrates the setting times of the concrete with SAF SP at different contents. Compared to the initial setting time and final

H. Zhao et al. / Construction and Building Materials 241 (2020) 118051

setting time of the control concrete (285 min, 413 min), the concrete mixtures with SAF SP have the long time to set. Moreover, the retardation on the setting times of the concrete depends on the amount of SAF SP in the concrete. 0.48 % SAF-1, SAF-2 SPs were incorporated into the concrete, the initial setting time and the final setting time of the concrete are prolonged by 170 min, 152 min and 147 min, 125 min, in comparison to the initial setting time and final setting time of the reference concrete. Beyond the certain dosage of SAF SP (0.48 %), the retarding effect of SAF-1, SAF-2 SPs on the setting times of the concrete becomes insignificant. It is accepted that -SO3H group in the molecule of SAF SP reacts with free Ca2+ in the solution of the concrete to form the unstable complex and the stable water film on the cement particle surface, which hinder the cement hydration process [36,37].Also, at the same amount of SP, the concrete with SAF-1 SP needs the longer setting times than that prepared by SAF-2 SP.

3.2.6. Wet density Fig. 8 presents that the wet density of the concrete mixtures with SAF-1, SAF-2 SPs of 0–0.72 % are in the ranges of 2328– 2361 kg/m3, 2328–2355 g/m3. The wet density of the concrete had a close relationship with the dosage and the synthetic method

Fig. 7. The setting times of the concrete with SAF-1, SAF-2 SPs at different dosages.

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of SAF SP. The inclusion of SAF SP in the concrete exhibits the higher the density of the concrete than the control concrete. The wet density values of the concrete mixtures with 0.48% SAF-1, SAF-2 SPs have an increase of 1.20 %, 0.86 %, in comparison to the concrete made without SAF SP. The content of SAF SP in the concrete is greater than 0.48 %, more SAF-1, SAF-2 SPs incorporating into the concrete can no increase anyway the wet density of the concrete. The related studies [38,39] indicated that the use of SAF SP in the concrete can more effective disperse the cement particle and reduces the void of the concrete. The structure of the concrete with SAF SP becomes more compact. Comparing the wet density values of the concrete with SAF SP at different synthetic methods, it is noted that the positive effect of SAF-1 SP on the wet density is the larger than that of SAF-2 SP. 3.2.7. Compressive strength The compressive strength development of the concrete mixtures with SAF SP of different dosages as a function of the curing period was shown in Fig. 9. From the test results obtained, it is found that the compressive strength of the control concrete, the SAF SP series concrete mixtures increase with the prolonging in the curing period from 3 days to 28 days. Moreover, due to the excellent dispersion ability of SAF SP for the cement particle, the introduction of SAF-1, SAF-2 SPs to the concrete reduces the water demand and improves the compressive strength of the concrete sample [40]. At the early curing stage (3 days), the concrete mixtures prepared by 0.16 %, 0.32 %, 0.48 % SAF-1, SAF-2 SPs exhibit

Fig. 8. The wet densities of the concrete with SAF-1, SAF-2 SPs at different dosages.

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7, 28 days of water-curing, the flexural strength of the concrete samples prepared by SAF-1, SAF-2 SPs of 0–0.72 % are in the ranges of 2.86–4.98 MPa, 4.12–7.82 MPa, 5.31–10.56 MPa and 2.86– 4.84 MPa, 4.12–7.41 MPa, 5.31–10.23 MPa. In general, regardless of the contents of SAF SP in the concrete, the flexural strength values of all the concrete grow with the lengthen of the curing time. Utilizing SAF SP in the concrete reduces the water demand in the concrete and increases the flexural strength of the concrete. For the concrete mixtures with 0.16 %, 0.32 %, 0.48 %, 0.64 %, 0.72 % SAF-1, SAF-2 SPs curing for 3 days, the flexural strength values of the concrete have an increase of 20.98 %, 42.66 %, 52.45 %, 65.73 %, 74.13 % and 14.68 %, 34.62 %, 48.25 %, 61.89 %, 69.23 %, in comparison to the concrete without SAF SP. During the change in the curing time form 3 days to 28 days, the SAF SP series concrete samples exhibit a faster increase rate in the flexural strength than the control concrete. The differences of the 28-days flexural strength between the control concrete and the SAF SP series concrete are more significant. The prolonging curing period was beneficial to improve on the long-term flexural strength of the SAF SPblended concrete. At the same amount of SAF SP, the concrete mixtures containing SAF-1 SP have the higher flexural strength than those with SAF-2 SP at the test periods of 3, 7, 28 days.

Fig. 9. The compressive strength development of the concrete with SAF-1, SAF-2 SPs at different dosages.

the compressive strength for 23.12 MPa, 25.99 MPa, 29.06 MPa and 22.29 MPa, 25.02 MPa, 28.11 MPa, which is 17.00–47.06 %, 12.80– 42.26 % higher than the control concrete (19.76 MPa). The content of SAF SP in the concrete mixture is higher than 0.48%, the large increase rate in the compressive strength (57.29%, 62.70% and 54.50%, 61.84%) was found in the 0.64%, 0.72% SAF-1, SAF-2 SPsblended concrete mixtures. Also, the prolonging curing period has a positive assistance on the long-term compressive strength of all the series concrete. After the concrete with SAF-1, SAF-2 SPs, ranging from 0 % to 0.72 %, were stored in water for 28 days, the compressive strength of the concrete with SAF SP of 0 %, 0.16 %, 0.32 %, 0.48 %, 0.64 %, 0.72 % experience an significant increase of 83.76 %, 90.96 %, 104.58 %, 108.43 %, 110.07 %, 111.91 % and 83.76 %, 89.95 %, 103.56 %, 106.65 %, 109.53 %, 110.23 %, compared with the 3-days compressive strength of the corresponding concrete. The compressive strength values of the SAF SP series concrete have a rapider increase than the control concrete. At a given content of SAF SP, because SAF-1 SP has the higher water-reducing rate than SAF-2 SP, at the same curing period, the contribution of SAF-1 SP on the compressive strength gain of the concrete is more significantly than SAF-2 SP. 3.2.8. Flexural strength The flexural strength test results of the SAF SP series concrete at different curing periods are given in Fig. 10. It is seen that, after 3,

Fig. 10. The flexural strength development of the concrete with SAF-1, SAF-2 SPs at different dosages.

H. Zhao et al. / Construction and Building Materials 241 (2020) 118051

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The same AOH, ACH2, AC@O, ASO3 functional groups are bonded in the molecules of SAF-1, SAF-2 SPs. The molecule of SAF-1 SP has the larger weight-average molecular weight (Mw), the number-average molecular weight (Mn), the polydispersity index (PDI) and the higher sulfonic group content than that of SAF-2. The inclusion of SAF SP in the concrete effectively lowers the water demand of the concrete. SAF-1, SAF-2 SPs of 0.32 %, 0.48 % were introduced to the concrete mixture, the large water- reducing percentages for 14.2 %, 19.2 % and 13.8 %, 18.6 % were achieved in the concrete, which had surpassed the value of 11 %, specified for type F SPs, according to ASTM C494 standard. Beyond the certain amount of SAF SP (0.48 %), more SAF-1, SAF-2 SPs incorporating into the concrete can no reduce anyway the water content in the concrete. The saturation dosage of SAF SP in this condition is 0.48 %. The utilization of SAF SP in the concrete improves fluidity preservation, increases the air content, the bleeding water rate, the setting times and the wet density of the concrete. With regard to the mechanical properties, the concrete prepared by SAF SP have the higher mechanical properties than the control concrete. The prolonging curing period has a positive assistance to enhance the long-term mechanical behaviors of the SAF SP-blended concrete samples.  At the same dosage, the SAF-1 SP series concrete have the larger water-reducing percentage, the lower slump loss rate, the larger bleeding water rate, wet density, the longer setting times, the higher mechanical properties than those containing SAF-2 SP. The differences in the air contents of the SAF-1, SAF-2 SPs series concrete are insignificant.  Using sodium pyrosulfite as sulfonating agent at four-step reaction processes is an effective method to synthesize SAF SP. CRediT authorship contribution statement Fig. 11. The ultrasonic pulse velocity of the concrete with SAF-1, SAF-2 SPs at different dosages.

Hui Zhao: Investigation, Methodology, Software, Writing review & editing. Ming Deng: Writing - original draft, Conceptualization. Mingshu Tang: Writing - original draft.

3.2.9. Ultrasonic pulse velocity Fig. 11 shows UPV values of the SAF SP-blended concrete at the curing periods of 3, 7, 28 days. It is found that, after the concrete mixtures with 0.16 %, 0.32 %, 0.48 %, 0.64 %, 0.72% SAF-1, SAF-2 SPs were stored in water for 3 days, UPV values of the concrete are 2826.7 m/s, 3112.6 m/s, 3598.3 m/s,3987.2 m/s, 3851.1 m/s and 2785.9 m/s,3015.5 m/s, 3314.6 m/s, 3644.3 m/s, 3775.6 m/s, it is 115.3–162.6 % and 113.6–154.0 % UPV value of the pure concrete (2451.4 m/s). Moreover, the presence of SAF-1, SAF-2 SPs in the concrete, ranging from 0.16 % to 0.72 %, causes a higher UPV value than the control concrete at the curing ages of 28, 90 days. Comparing Fig. 11 (a), (b), it is seen that, at the same dosage and the same curing period, the SAF-1 SP series concrete seems to be more effective in enhancing UPV value than the SAF-2 SP series concrete.

Declaration of Competing Interest

4. Conclusions Nowadays, Superplasticizers (SPs) have been recognized as the important component to prepare the concrete materials due to its excellent water-reducing ability. In this study, the water-soluble sulfonated acetone-formaldehyde (SAF) SP was produced at different synthetic methods (SAF-1, SAF-2). The molecular structures and the application properties of SAF-1, SAF-2 SPs in the concrete were tested and compared. The following test results can be obtained.

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. Acknowledgements This project was supported by western traffic science and technology projects (Chinese, No. 2006ZB01-2).The authors would like to thank Prof Wei Sun of Southeast University in China. His sponsorship and support made this study possible. References [1] L. Czarnecki, W. Kurdowski, S. Mindes, in: Developments in the Formulation and Reinforcement of Concrete, Woodhead Publishing, UK, 2008, pp. 270–284. [2] P.-C. Aïtcin, J.R. Flatt, in: Science and technology of concrete admixtures, Woodhead Publishing, UK, 2015, pp. 1315–1412. [3] D. Wilinski, P. Lukowski, G. Rokicki, Polymeric superplasticizers based on polycarboxylates for ready-mixed concrete: current state of the art, Polimery 61 (7–8) (2016) 474–481. [4] A. Tajbakhshian, R.M. Saeb, H.S. Jafari, F. Najafi, H.A. Khonakdar, M. Ayoubi, F.H. Asi, High-performance carboxylate superplasticizers for concretes: Interplay between the polymerization temperature and properties, J. Appl. Polym. Sci. 134 (23) (2017) 449–508. [5] S. Chandra, J. Bjornstrom, Influence of superplasticizer type and dosage on the slump loss of Portland cement mortars-Part II, Cem. Concr. Res. 32 (10) (2002) 1613–1619.

10

H. Zhao et al. / Construction and Building Materials 241 (2020) 118051

[6] S.N. Sha, M. Wang, C.J. Shi, Y.C. Xiao, Influence of the structures of polycarboxylate superplasticizer on its performance in cement-based materials-A review, Constr. Build. Mater. 233 (10) (2019) 1–13. [7] S.H. Patel, C.B. Dixit, B.R. Dixit, Acetone-formaldehyde-resorcinol-based IPNs and their glass-fiber-reinforced composites, Polym-Plast. Technol. Eng. 40 (1) (2001) 53–63. [8] R. Li, J.D. Yang, M.H. Lou, S.M. Zhou, Q.X. Qiu, Influence of sulfonated acetone formaldehyde condensation used as dispersant on low rank coal-water slurry, Energ. Convers. Manage. 64 (3) (2012) 139–1449. [9] H.V. Daake, D. Stephan, Performance enhancement of polycondensate-based superplasticizers by encapsulation, Chem. Eng. Technol. 40 (3) (2017) 608–615. [10] M. Pei, Y. Yang, X. Zhang, J. Zhang, J. Dong, Synthesis and the effects of watersoluble sulfonated acetone-formaldehyde resin on the properties of concrete, Cem. Concr. Res. 34 (8) (2004) 1417–1420. [11] H. Lou, K. Ji, H. Lin, Y. Pang, Y. Deng, X. Qiu, B.H. Zhang, G.Z. Xie, Effect of molecular weight of sulphonated acetone-formaldehyde condensate on its adsorption and dispersion properties in cementitious system, Cem. Concr. Res. 42 (8) (2012) 1043–1048. [12] M. Pei, Y. Yang, X. Zhang, J. Zhang, Y. Li, Synthesis and properties of watersoluble sulfonated acetone-formaldehyde resin, J. Appl. Polym. Sci. 91 (5) (2004) 3248–3250. [13] ASTM C 150-07. Standard specification for portland cement, American Society of Testing Materials., West Conshohocken, USA, 2007. [14] GOST 10180. Concretes. Methods for strength determination using reference specimens, Gosudarstvennye Standarty State Standard., Moscow, Russian, 1999. [15] GB/T 8076. Standard for Test Method of Performance on the concrete admixtures, National Standards of the People’s Republic of China., Beijing, China, 2008. [16] BS EN 12350-2.Testing fresh concrete. Slump test, British Standards Institution., London, UK, 2000. [17] BS EN 12350-7.Testing fresh concrete. Air content-Pressure methods, British Standards Institution., London, UK, 2000. [18] BS EN 480-4. Admixtures for concrete, mortar and grout: Test methodsdetermination of bleeding of concrete, British Standards Institution., London, UK, 2004. [19] BS EN 480-2. Admixtures for concrete, mortar and grout: Test methodsDetermination of setting time, British Standards Institution., London, UK, 2006. [20] BS EN 12350-6. Testing fresh concrete. Density, British Standards Institution., London, UK, 2000. [21] BS EN 12390-3.Testing hardened concrete. Method of determination of compressive strength of concrete cubes, British Standards Institution., London, UK, 2000. [22] BS EN 12390-5.Testing hardened concrete: Flexural strength of test specimens, British Standards Institution., London, UK, 2000. [23] ASTM C 597-02. Standard test method for pulse velocity through concrete, American Society of Testing Materials., West Conshohocken, USA, 2002. [24] H.W. Zhao, B. Liao, F. Nian, K. Wang, Y. Guo, H. Pang, Investigation of the clay sensitivity and cement hydration process of modified HPEG-type polycarboxylate superplasticizers, J. Appl. Polym. Sci. 56 (9) (2018) 465–472.

[25] F. DugonjiC-BiliC, J. Plank, Polyelectrolyte complexes from polyethylene imine/ acetone formaldehyde sulfite polycondensates: a novel reagent for effective fluid loss control of oil well cement slurries, J. Appl. Polym. Sci. 121 (3) (2011) 1262–1275. [26] T. Zhang, J. Gao, X. Deng, Y. Liu, Graft copolymerization of black liquor and sulfonated acetone formaldehyde and research on concrete performance, Constr. Build. Mater. 83 (6) (2015) 308–313. [27] M.A.A. Mahmoud, H.S.M. Shehab, S.A. El-Dieb, Concrete mixtures incorporating synthesized sulfonated acetophenone-formaldehyde resin as superplasticizer, Cem. Concr. Compos. 32 (5) (2010) 392–397. [28] ASTM C 494. Standard Specification for Chemical Admixtures for Concrete. American Society of Testing Materials., West Conshohocken, USA, 1999. [29] C.M. Childs, K.M. Perkins, A. Menon, N.R. Washburn, Interplay of Anionic Functionality in Polymer-Grafted Lignin Superplasticizers for Portland Cement, Ind. Eng. Chem. Res. 58 (43) (2019) 19760–19766. [30] M. Zhou, X. Qiu, D. Yang, H. Lou, X. Ouyang, High-performance dispersant of coal-water slurry synthesized from wheat straw alkali lignin, Fuel. Process. Technol. 88 (4) (2007) 375–382. [31] B.G. Ma, H.H. Qi, H.B. Tan, Y. Su, X.G. Li, X.H. Liu, C.B. Li, T. Zhang, Effect of aliphatic-based superplasticizer on rheological performance of cement paste plasticized by polycarboxylate superplasticizer, Constr. Build. Mater. 233 (56) (2019) 1–9. [32] H.J. Peng, D.J. Qu, X.J. Zhang, F.M. Chen, T. Wan, Adsorption characteristics of water- reducing agents on gypsum surface and its effect on the rheology of gypsum plaster, Cem. Concr. Res. 35 (3) (2005) 527–531. [33] BS EN 934-2. Admixtures for concrete, mortar and grout. Concrete admixtures. Definitions, requirements, conformity, marking and labeling. British Standards Institution., London, UK, 2009. [34] J. Szwabowski, B. Łazniewska-Piekarczyk, Air-entrainment problem in selfcompacting concrete, J. Civ. Eng. Manag 15 (2) (2009) 137–147. [35] H.J. Kim, J.H. Yim, H.S. Kwon, Quantitative measurement of the external and internal bleeding of conventional concrete and SCC, Cem. Concr. Compos 54 (6) (2014) 34–39. [36] H.S. Tantawi, Effect of different types of concrete polymer admixtures on physicochemical and mechanical properties of cement pastes, Polym-Plast. Technol. Eng 36 (6) (1997) 863–872. [37] M.H. Lou, R.H. Lai, X.M. Wang, X.Y. Pang, J.D. Yang, Q.X. Qiu, B. Wang, B.H. Zhang, Preparation of lignin-based superplasticizer by graft sulfonation and investigation of the dispersive performance and mechanism in a cementitious system, Ind. Eng. Chem. Res. 52 (46) (2013) 16101–16109. [38] G.L. Li, H.K.A. Kwan, Effects of superplasticizer type on packing density, water film thickness and flowability of cementitious paste, Constr. Build. Mater. 86 (11) (2015) 113–119. [39] X.P. Wang, R. Yu, Q.L. Song, Z.H. Shui, Z. Liu, S. Wu, D.S. Hou, Optimized design of ultra- high performance concrete (UHPC) with a high wet packing density, Cem. Concr. Res. 126 (7) (2019) 1613–1619. [40] R. Wang, J. Li, T. Zhang, L. Czarnecki, Chemical interaction between polymer and cement in polymer-cement concrete, B. Pol. Acad. Sci-Tech. 64 (4) (2016) 661–663.