The Synthesis and Performance of a Novel Lignin Modified Salt Resistance Branched High-Performance Water Reducer

1. Introduction

The water reducer is a crucial admixture in the concrete industry, which has witnessed a shift from the conventional polyelectrolyte water reducer to the polycarboxylic acid water reducer [1,2,3,4,5,6]. The comb type polycarboxylic acid water reducer, characterized by its remarkable adjustability and significant potential for achieving high performance, effectively addresses concerns related to dispersibility and stability, thereby yielding exceptional application outcomes [7,8,9].

However, it is impossible to directly use seawater, saline water, and alkali water to build coastal wave-resistant dikes and saltwater lake dams due to the decreased flow ability induced by salt resistance, which requires long-distance transportation of fresh water increasing costs and fuel consumption during transportation.

Salt resistant water reducer could effectively increase flow ability of concrete slurry containing salt which could help the direct prepare of slurry by seawater,saline water, and alkali water.

This study is still in its early stages, and there is no relevant research yet. The available salt-resistant water reducer literatures are mostly about resistance of erosion of concrete by sulfate and chloride salts after being added [10,11,12,13], rather than to improve its fluidity during construction. Starting from the multi-hydroxyl lignin, a salt resistance branched high-performance water reducer (BHPWR) was prepared by introducing branching structures. The main chain contained carboxyl and sulfonic acid groups as well as long hydrophilic side chains. By utilizing the strong steric hindrance effect, the volume dispersion and electrostatic repulsion lead to Strong dispersing effect which could improve concrete fluidity under saline conditions.

2. Materials and Methods

2.1. Materials

Acrylic acid was obtained from Sinopharm Chemical Reagent Co., Ltd. AMPS was obtained from Nanjing All-Plus chemical Co. Ltd. APEG-2000 was obtained from Haian Petrochemical Plant Co. Ltd. Lignin was obtained from Shandong Gaotang Polymeric Lignin Co., Ltd.

Base Cement: Jidong Cement Co. Ltd provided P·O 52.5 Cement. Hebei Huakai Mining Co. Ltd supplied Quartz Sand ranging from 20 to 120 mesh. Gansu Sanyuan Silicon Material Co., Ltd provided Silica fume with a SiO2 content exceeding 94% and a specific surface area of 20 m2/g. Shandong Shunke Building Materials Technology Co., Ltd supplied Class I fly ash with a density of 2200 kg/m3. Xingtai Guangqing Refractory Material Distribution Co., Ltd provided Glass bead with a density of 412 kg/m3 and a particle size of approximately 0.1 mm. Changzhou Tianyi Engineering Fiber Co., Ltd supplied Steel Fiber with a diameter of 0.22 mm and a length ranging from 13 to 15 mm. Jiangsu Liqi Environmental Technology Co., Ltd provided the defoaming agent.

2.2. Characterization

The Bruker Tensor 27 spectrometer was used to record Fourier transform infrared (FTIR) spectra of the BHPWR in KBr pellets at room temperature. The spectra were recorded in the range of 4000-400 cm^-1.

The Scanning Electron Microscope (SEM) measurement was obtained using an JEOL JSM-7600 Thermal Field Emission Scanning Electron Microscope, and the surface of the gel particles was treated with gold spraying previously.

The consistency of cement paste was examined following the guidelines of GB 8077-2012 'Test Method for Consistency of Concrete Admixture' using a water-to-cement ratio of 0.29, and the solid content of the water reducing agent was 0.12%.

The water reduction rate was tested according to GB 8076-2008 "Concrete Admixtures". The concrete mix ratio is: m (Jidong Cement): m (sand): m (stone) = 360: 810: 990.

Concrete viscosity was tested according to T500 in JGJ/T 283-2012 "Technical Specification for Application of Self-Compacting Concrete".

The mechanical properties of concrete are tested in accordance with the GB/T 50081-2019 standard through the process of standard steam curing. The specimens, after being exposed to an experimental setting for 24 hours at a temperature of (20±5)℃ and a relative humidity above 50%, are transferred to a curing box. They are then gradually heated, not surpassing a rate of 15℃/h, until reaching a temperature of (90±1) ℃. The specimens are maintained at a constant temperature for 48 hours before being cooled down, again not exceeding a rate of 15℃/h, until reaching (20±5) ℃.

The process of curing at the typical temperature of a room is conducted in accordance with the guidelines provided by GB/T 50081-2019, which outlines the standard procedures for evaluating the mechanical properties of concrete. Samples are placed in a typical curing chamber at a temperature of (20±2) ℃ and a relative humidity exceeding 95%.

A ZNN-D6 rotational viscometer was used to conduct the rheological test at 85℃ and atmospheric pressure, following the guidelines of SY/T 5504.3-2008 "Evaluation Method for Oil Well Cement Additives Part 3 Friction Reducers".

The thickening test was conducted according to GB/T19139-2012 "Test Methods for Oil Well Cement" using an OWC-9480C pressurized thickening meter.

3. Synthesis and Characterization of BHPWR

3.1. The Synthesis of BHPWR

Five BHPWR samples were produced through the process of free radical polymerization. 2-acrylamide-2-methylpropanesulfonic acid (AMPS) (100g, 0.48mol), acrylic acid (15 g, 0.21mol), allyl polyethylene glycol APEG-2000 (10 g, 0.0050mol), Lignin (0.5 g for BHPWR-1, 0.7 g for BHPWR-1, 0.9 g for BHPWR-1, 1.1 g for BHPWR-1, and 1.3 g for BHPWR-1,) and water (375 g) were added in one portion and stirred to dissolve at 70 ℃, then Initiator was added and the solution was kept warm at 70 ℃ for 3 h. Resulting pale yellow liquid was filtered while still hot. In this system, the presence of acrylic acid enhances the attachment of dispersant to cement particles, resulting in three-dimensional dispersion effects when combined with APEG-2000 and lignin, while AMPS provides resistance to salt.

3.2. The Characterization of BHPWR

The IR spectrum of the dispersant is presented in Figure 1, with the main absorption bands of the dispersant assigned as follows: a) OH stretching (H₂O, APEG-2000) at 3500 cm^-1, b) CH₂ and CH₃ stretching (AMPS, APEG-2000, lignin) at 2880 cm^-1, c) C=O symmetric stretching (acrylic acid) at 1720 cm^-1, d) Aromatic ring skeleton stretching (lignin) at 1653 cm^-1 and 1467 cm^-1, e) COO-symmetric stretching (acrylic acid) at 1345 cm^-1, f) C-O-C stretching (APEG-2000, lignin) at 1114 cm^-1, and g) S-O bending (sulfonic acid group of AMPS) at 626 cm^-1.

Electron microscopy tests were conducted to further study the stereostructure of water reducer in solution, using scanning electron microscopy (SEM). BHPWR does not exhibit a single regular shape due to the free rotation of its main chain and side chains. In addition, due to the thermal motion of molecules, the shape of water reducer is constantly changing. Despite the adsorption of the primary chain onto the cement particle surface in cement slurry, the secondary chain exhibits erratic movement as well. Figure 2 shows the aggregate state of water reducer at the micrometer scale, which is a dendritic shape. The primary chain of the polymer attaches to the cement particles in the cement slurry through carboxyl and sulfonic acid groups, while the polymer's secondary chains are long side chains that can extend without restriction when the primary chain is attached to the cement slurry. The response of water and mechanical radius increases due to the significant molecular weight of the side chains, resulting in a substantial spatial steric hindrance. Due to this large spatial steric hindrance effect, the side chains have strong three-dimensional dispersing ability on cement particles, which leads to good dispersion of cement slurry and further increases its rheology.

4. Concrete and Cement Slurry Performance

4.1. Concrete Performance

Table 1 and Table 2 displayed the performance of concrete made with freshwater and saltwater, correspondingly. The water-reducing rate of BHPWR-3 can reach up to 45% in fresh water and 44% in saline water, and its large spatial steric hindrance improves the dispersibility of the water reducer, achieving high water reduction and low viscosity. In addition, its compressive strength is the highest after 3-day curing and 3, 7, 28-day standard curing, and it has the best overall performance both in fresh water and saline water prepared systems.

4.2. Cement Slurry Performance

BHPWR could also be used as oil cement dispersant. BHPWR-3 was added to the slurry prepared with fresh water, saline water with 36 % NaCl by weight of water, and substitute ocean water which is prepared according to Designation D1141-98 (D1141-98). The dispersant underwent evaluation in accordance with SY/T 5504.3-2008 and the important indicators are flow behavior index n and consistency index K calculated from θ₃₀₀ and θ₃₀₀, the reading of viscometer at the shearing rate of 100 r/min and 300 r/min. Good dispersant should result to bigger n and lower k.

$$n=2.096\times \mathit{lg}\frac{{\theta }_{300}}{{\theta }_{100}}$$

(1)

$$K=\frac{0.511\times {\theta }_{300}}{511^n}$$

(2)

Rheology of slurries prepared with fresh water, saline water, and substitute ocean water is listed in Table 3. With the addition of 1.5 %BWOC, n = 0.78-0.93 and K = 0.04-0.16 Pa.sⁿ at 52 ℃ and atmospheric pressure while n = 0.73-0.92 and K =0.16-0.19 Pa.sⁿ at 85 ℃ and atmospheric pressure, which indicates that BHPWR-3 exhibits good dispersibility in fresh water, saline water, and substitute ocean water.

5. The Application of BHPWR

The cement slurries used in Iraq's Halfaya and Missan Oilfield are prepared by saline water with low fluidity, significant thixotropy, and high initial consistency due to its high solid and salt content.

Furthermore, the elevated temperature during the summer in Iraq speeds up the process of cement hydration, ultimately causing a decrease in the rheology of the cement slurry. Due to the persistent high ground temperature, which can reach up to 60℃ during the summer in Iraq, the cement slurry experienced significant hydration while being mixed, leading to a decrease in its fluidity as shown in Table 4 which shows θ₃₀₀ unreadable at 60 ℃, strong thixotropy and high initial consistency leading to difficulty in pumping and unstable density which seriously impacts on on-site construction safety and cementing quality.

BHPWR could enhance the flow characteristics of slurry, making it easier to mix and place. Rheology is a metric that gauges the ability to resist fluid motion and the decrease in such resistance when subjected to pressure. Upon substitution of the dispersant in Table 5 with BHPWR-3, the slurry displayed favorable rheological characteristics, with a flow behavior index of n=0.74 and a consistency factor of K=1.08 Pa.sⁿ at 60 ℃ from which we can learn that the BHPWR-3 is a kind of good performance dispersant.

To cement the 244.5 mm salt paste layer casing for five wells in Halfaya and Missan Oilfield in Iraq, the BHPWR-3 was utilized with high-density (2.28 g cm^-3) saline cement slurry under the ambient temperature of 55-58 ℃. It is worth noting that over 85% of each cementing job executed was deemed outstanding. One of the wells, namely FQCS-44H, serves as a prime example, involving the sealing of the Lower Fars formation containing high-pressure saltwater zones via casing measuring 244.5 mm in diameter placed in 311.1 mm open holes, with the shoe being at 2957.7 m as opposed to the previous 339.7 mm casing at 2081.5 m. However, it is challenging to conduct cementing under these circumstances given that higher mud weight (2.23 g cm^-3) requires denser slurry, potentially narrowing the cementing window. Despite these complications, the Segment Bond Tool evaluation indicates that the cementing job was qualified at 100%, with 85% of the job regarded as excellent.

6. Conclusions

BHPWR prepared via free radical polymerization demonstrates excellent performance as a water reducer, with reduction rates of up to 45% in fresh water and 44% in saline water. After 3-day curing and standard curing for 3, 7, and 28 days, it shows the highest compressive strength and overall best performance in both water and saline water systems. Furthermore, it has been found to exhibit good dispersibility in fresh water, saline water, and substitute ocean water, making it a suitable dispersant for oil cement slurries. Rheological testing of slurries prepared with BHPWR-3 showed n=0.78-0.93 and K=0.04-0.16 Pa.sⁿ at 52 ℃ and atmospheric pressure, and n=0.73-0.92 and K=0.16-0.19 Pa.sⁿ at 85 ℃ and atmospheric pressure. This indicates that BHPWR-3 is effective in fresh water, saline water, and substitute ocean water. In the Halfaya and Missan Oilfields of Iraq, BHPWR was used in slurry with a density of 2.28g cm^-3 for casing the 244.5 mm salt paste layer of five wells. Cementing results exceeded expectations with over 85% excellent and 100% qualified.