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With the continuous expansion of China’s basic economic construction, resources such as sand and stone are becoming increasingly scarce and vary significantly in quality. Concrete slump often decreases rapidly. To address this issue, domestic concrete companies generally add polycarboxylate superplasticizers, which are highly sought after for their low dosage, good slump retention, and compatibility with various concrete admixtures.
In recent years, experimental research on EPEG 3000 polycarboxylate water reducer liquid has become increasingly widespread because it has higher double-bond reactivity than general macromonomers, polymerizes more easily, has a shorter polymerization time, and delivers good performance, which supports energy-saving, environmental protection, and green production.
This article mainly uses ethylene glycol monovinyl polyoxyethylene ether (EPEG), hydroxyethyl acrylate (HEA), and acrylic acid (AA) as monomers, vitamin C (Vc)/hydrogen peroxide (HO) as the initiator system, mercaptoethanol (ME) as the chain transfer agent, and polymerization reaction to obtain an EPEG 3000 polycarboxylate water reducer liquid.
Add EPEG and distilled water to the installed four-necked flask, turn on the stirrer and observe until the polyether dissolves evenly. The starting temperature is controlled between 15 ℃ and 45 ℃. Mix hydrogen peroxide with distilled water to form material A; mix mercaptoethanol with vitamin C and distilled water to form material B; mix hydroxyethyl acrylate with acrylic acid and distilled water to form material C; then add dropwise for 0.9 h to 1.1 h. After dripping and holding for 0.8 h, adjust the mother liquor pH to 5-7 with a 32% NaOH solution to prepare the target sample, LZKZJ-6, a six-carbon polycarboxylate slump protector.
The results from 5℃ to 70℃ show that the optimal starting temperature range is 15 ℃ to 45 ℃. The main reason is that a starting temperature that is too low makes the monomer difficult to dissolve and the solution uneven, resulting in uneven polymerization. If the starting temperature is too high, the six-carbon monomer becomes highly active, which can easily lead to self-polymerization and affect product performance.
The results for drop times from 0.5 to 1.5 h show that the best drop time range is 0.9 to 1.1 h. The main reason is that the polymerization conversion rate of the hexacarbon monomer is high within one hour; however, too short a time and too fast a polymerization speed can easily produce gel, and too long a polymerization time can affect the product conversion rate.
The research results on the chain transfer agent from 0.20% to 0.80% of EPEG are shown in Figure 3. The experiment shows that the optimal dosage range of the chain transfer agent is 0.50% to 0.60% of EPEG. This is because the chain transfer agent promotes molecular chain transfer during polymerization. If the amount is too small, a macromolecular gel can form easily. If the amount is too large, the polymer molecular weight becomes too low, affecting product performance.
The research results on acrylic acid AA from 3% to 8% of EPEG show that the optimal dosage range of acrylic acid AA is 5% to 6% of EPEG. The main reason is that when the amount of acrylic acid AA is too small, the molecular weight of the synthesized polycarboxylic acid is too low, the polymerization rate is low, and the monomer reaction is incomplete; when the amount of acrylic acid AA is too large, the molecular weight of the polycarboxylic acid is too large, which is not conducive to dispersion and affects product performance.
Research on small-monomer HEA at 11% to 16% of EPEG shows that the optimal dosage range is 13% to 14% of EPEG. The main reason is that when the small-monomer HEA content is too low, alkaline hydrolysis of hydroxyethyl acrylate is insufficient to achieve good slump retention. When the amount of small-monomer HEA is too high, the polycarboxylic acid’s molecular weight becomes too large, hindering dispersion and affecting product performance.
The results show that reducing agent Vc at 0.1% to 0.35% of EPEG yields an optimal dosage range of 0.2% to 0.25% of EPEG. The main reason is that the reducing agent Vc and the oxidant produce free radicals through a redox reaction, initiating monomer polymerization. If the amount is too small, the degree of polymerization is low; if the amount is too large, the reaction rate is accelerated too fast, and gel is likely to be generated, which affects the product performance.
The research results on oxidant HO at 0.7% to 1.30% of EPEG show that the optimal dosage range is 0.90% to 1.10% of EPEG. The main reason is that the oxidant HO and the reducing agent produce free radicals through a redox reaction, initiating monomer polymerization. If the amount is too small, the degree of polymerization is low; if the amount is too large, the reaction rate is accelerated too fast, and it is easy to produce gel, which affects the product performance.
The concrete performance test used a C30 mix with a C:S:G: W ratio of 1:2.1:2.9:0.5. LZKZJ-6 and PCE-5 were compounded with PCE-4 and H (additives), with LZKZJ-6 used at 94% of the PCE-5 dosage. The concrete performance comparison test was conducted at the same dosage.
The results showed that at 94% of the PCE-5 dosage, the initial slump/expansion of LZKZJ-6 concrete was equivalent to PCE-5; the 1-hour and 2-hour slump/expansion of LZKZJ-6 concrete were better than PCE-5; and the compressive strength of the concrete was high. From this, it can be seen that LZKZJ-6 has the advantages of low dosage, good slump retention, and high compressive strength.
This article studies the main factors of EPEG 3000 polycarboxylate water reducer liquid. It determines the optimal process for preparing EPEG 3000 polycarboxylate slump reducer as follows: starting temperature of 15 ℃~45 ℃, chain transfer agent dosage of 0.50%~0.60% of EPEG, small monomer AA dosage of 5%~6% of EPEG, small monomer HEA dosage of 13%~14% of EPEG, reducing agent Vc dosage of 0.20%~0.25% of EPEG, oxidant HO dosage of 0.90%~1.10% of EPEG, copolymerization reaction time of 0.9h~1.1h, and insulation reaction of 0.8h.
The EPEG 3000 polycarboxylate water reducer produced in this study has excellent liquid properties, with advantages such as low dosage, good slump retention, and high compressive strength.
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