Background
The cement dispersant, also called water reducing agent, can reduce the mixing water consumption of concrete under the condition of not influencing the fluidity of the concrete, or increase the fluidity of concrete mixture under the condition of not influencing the water consumption, or both, and is an additive with the functions of reducing water and enhancing. The cement dispersant is mainly used in engineering for reducing water consumption of concrete, lowering water cement ratio, saving cement and improving workability.
After the cement dispersant is applied, the flowability and strength of concrete can be greatly improved, and thus the engineering quality is improved. Concrete is the most used building material in the world, and cement dispersant has become an essential additive in concrete production. At present, in developed countries and regions, the amount of cement dispersant in concrete is more than 80%. The cement dispersant mainly comprises the following components: a modified lignosulfonate water reducing agent; a naphthalenesulfonic acid formaldehyde condensate water reducing agent; a melamine water reducing agent; a sulfamate water reducing agent; an aliphatic water reducing agent; a carboxylic acid graft copolymer water reducing agent.
The polycarboxylate graft copolymer water reducing agent is a novel high-performance water reducing agent at present, and has the following advantages: high water reducing rate, small slump loss and high later strength: the 28d strength increase is more than 40%. The mixing amount is small, and is generally below 1%. Although the Zeta potential value of the surface of cement particles of the cement paste mixed with the water reducing agent is smaller than that of naphthalene series or melamine, the slump constant is not lost basically within 1-2 hours. The reason for this is that the carboxylate ions react with Ca in the cement paste2+In combination, the hydration rate is slowed down without a rapid decrease in the water reducer concentration due to the relatively small amount of hydrate. In addition, the main side chain molecular structure form of the polycarboxylate is determined to be three-dimensional zigzag adsorption on the cement surface, which is different from the horizontal adsorption mode of naphthalene series, so that the polycarboxylate has a three-dimensional potential protection effect and can keep a dispersion stable state for a long time. The water reducing agent is suitable for high-performance concrete. Its disadvantages are: poor compatibility and poor predictability in concrete, such as: when the polycarboxylic acid water reducing agent is used together with other additives, the concrete slump loss is too fast, the phenomena of quick hardening and the like easily occur, and the compatibility problem of cement and chemical additives exists; in concrete using a high performance water reducing agent, when the slump increases as the unit water amount decreases, the following problems often occur: the water reducing agent consumption is too large, the concrete viscosity is too large, the segregation and bleeding phenomena occur, and the pumping is difficult. And the polycarboxylic acid water reducing agent has complex synthesis process and expensive raw materials.
Disclosure of Invention
The technical problem to be solved is as follows: aiming at the technical problems, the invention provides a preparation method of a modified cement dispersant, which has the advantages of low energy consumption, low production cost and the like, and the prepared dispersant can improve various performances of concrete, has no pollution to the environment and is harmless to human bodies.
The technical scheme is as follows: a preparation method of a modified cement dispersant, comprising the following steps:
step one, weighing 8-12 parts by mass of nano titanium dioxide, adding 30-50 parts by mass of polyoxyethylene monomethyl ether methacrylate and 60-80 parts by mass of 5 vt.% HCl solution, and heating in a water bath at 80-90 ℃ for 1-2 hours under the condition of magnetic stirring;
step two, cooling the mixture to room temperature after heating, then carrying out centrifugal separation at the rotating speed of 500-650 r/min, washing the mixture after centrifugal separation with deionized water, and drying to obtain the nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate;
taking 3-5 parts by mass of acrylic acid, 4-6 parts by mass of calcium lignosulfonate, 0.2-0.6 part by mass of nano silicon powder and 70-90 parts by mass of 75wt.% ethanol, heating to 50-60 ℃ under the conditions of stirring and nitrogen filling, and reacting for 30-45 min;
adding 20-30 parts by mass of the nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate dried in the second step and 2-6 parts by mass of 5wt.% ammonium persulfate aqueous solution into the reacted mixture, and heating to 70-80 ℃ to react for 3-5 h;
and step five, after the reaction is finished, neutralizing the reaction product by using a 30wt.% NaOH solution until the pH value is 7, and finally obtaining the modified cement dispersant.
Preferably, the nano titanium dioxide in the first step is rutile type nano titanium dioxide, and the particle size is 20-50 nm.
Preferably, in the step one, 10 parts by mass of nano titanium dioxide is weighed, 45 parts by mass of polyoxyethylene monomethyl ether methacrylate and 70 parts by mass of 5 vt.% HCl solution are added, and then the mixture is heated in a water bath at 85 ℃ for 1.5 hours under the condition of magnetic stirring.
Preferably, in the second step, after the mixture is heated, the mixture is cooled to room temperature, then centrifugal separation is carried out at the rotating speed of 600r/min, and the mixture after centrifugal separation is washed by deionized water and then dried to obtain the nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate.
Preferably, the particle size of the nano silicon powder in the third step is 100-200 nm.
Preferably, in the third step, 4 parts by mass of acrylic acid, 5 parts by mass of calcium lignosulfonate, 0.4 part by mass of nano silicon powder and 85 parts by mass of 75wt.% ethanol are taken, stirred and filled with nitrogen, heated to 55 ℃ and reacted for 40 min.
Preferably, in the fourth step, 25 parts by mass of the dried nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate in the second step and 4 parts by mass of a 5wt.% ammonium persulfate aqueous solution are added into the mixture after the reaction, and then the temperature is raised to 75 ℃ for reaction for 4 hours.
Has the advantages that: the modified cement dispersant prepared by the method is liquid, is dripped into the clinker at a uniform speed during the conveying of the clinker, and the clinker is rapidly dispersed, so that the service life of the ball mill can be prolonged, and the energy consumption and the production cost are reduced. The dispersant can improve various performances of concrete, has no pollution to the environment and is harmless to human bodies. The nanometer titanium dioxide modified polyoxyethylene monomethyl ether methacrylate, acrylic acid, calcium lignosulfonate, nanometer silane and ethanol are mixed, and especially, nanometer silicon powder is added to play a role in synergy, so that the dispersibility of the modified cement dispersant prepared by the invention on cement is greatly improved.
Detailed Description
Example 1
A preparation method of a modified cement dispersant, comprising the following steps:
step one, weighing 8 parts by mass of nano titanium dioxide, adding 30 parts by mass of polyoxyethylene monomethyl ether methacrylate and 60 parts by mass of 5 vt.% HCl solution, and heating in a water bath at 80 ℃ for 1h under the condition of magnetic stirring, wherein the nano titanium dioxide is rutile type nano titanium dioxide, and the particle size is 20-50 nm.
And step two, cooling the mixture to room temperature after heating, then carrying out centrifugal separation at the rotating speed of 500r/min, washing the mixture after centrifugal separation by using deionized water, and drying to obtain the nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate.
And thirdly, heating 3 parts by mass of acrylic acid, 4 parts by mass of calcium lignosulfonate, 0.2 part by mass of nano silicon powder and 70 parts by mass of 75wt.% ethanol to 50 ℃ under the conditions of stirring and nitrogen filling, and reacting for 30min, wherein the particle size of the nano silicon powder is 100-200 nm.
And step four, adding 20 parts by mass of the dried nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate in the step two and 2 parts by mass of a 5wt.% ammonium persulfate aqueous solution into the reacted mixture, and then heating to 70 ℃ for reaction for 3 hours.
And step five, after the reaction is finished, neutralizing the reaction product by using a 30wt.% NaOH solution until the pH value is 7, and finally obtaining the modified cement dispersant.
Example 2
A preparation method of a modified cement dispersant, comprising the following steps:
step one, weighing 12 parts by mass of nano titanium dioxide, adding 50 parts by mass of polyoxyethylene monomethyl ether methacrylate and 80 parts by mass of 5 vt.% HCl solution, and heating in a water bath at 90 ℃ for 2 hours under the condition of magnetic stirring, wherein the nano titanium dioxide is rutile type nano titanium dioxide, and the particle size is 20-50 nm.
And step two, cooling the mixture to room temperature after heating, then performing centrifugal separation at the rotating speed of 650r/min, washing the mixture after centrifugal separation by using deionized water, and drying to obtain the nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate.
And step three, taking 5 parts by mass of acrylic acid, 6 parts by mass of calcium lignosulphonate, 0.6 part by mass of nano silicon powder and 90 parts by mass of 75wt.% ethanol, heating to 60 ℃ under the conditions of stirring and nitrogen filling, and reacting for 45min, wherein the particle size of the nano silicon powder is 100-200 nm.
And step four, adding 30 parts by mass of the dried nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate in the step two and 6 parts by mass of a 5wt.% ammonium persulfate aqueous solution into the reacted mixture, and then heating to 80 ℃ for reaction for 5 hours.
And step five, after the reaction is finished, neutralizing the reaction product by using a 30wt.% NaOH solution until the pH value is 7, and finally obtaining the modified cement dispersant.
Example 3
A preparation method of a modified cement dispersant, comprising the following steps:
step one, weighing 10 parts by mass of nano titanium dioxide, adding 45 parts by mass of polyoxyethylene monomethyl ether methacrylate and 70 parts by mass of 5 vt.% HCl solution, and heating in a water bath at 85 ℃ for 1.5h under the condition of magnetic stirring, wherein the nano titanium dioxide is rutile type nano titanium dioxide, and the particle size is 20-50 nm.
And step two, cooling the mixture to room temperature after heating, then carrying out centrifugal separation at the rotating speed of 600r/min, washing the mixture after centrifugal separation by using deionized water, and drying to obtain the nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate.
And thirdly, heating 4 parts by mass of acrylic acid, 5 parts by mass of calcium lignosulfonate, 0.4 part by mass of nano silicon powder and 85 parts by mass of 75wt.% ethanol to 55 ℃ under the conditions of stirring and nitrogen filling, and reacting for 40min, wherein the particle size of the nano silicon powder is 100-200 nm.
And step four, adding 25 parts by mass of the dried nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate in the step two and 4 parts by mass of a 5wt.% ammonium persulfate aqueous solution into the reacted mixture, and then heating to 75 ℃ to react for 4 hours.
And step five, after the reaction is finished, neutralizing the reaction product by using a 30wt.% NaOH solution until the pH value is 7, and finally obtaining the modified cement dispersant. Comparative example 1
The difference from example 3 is that no nano silicon powder is added, and the specific preparation process is as follows:
step one, weighing 10 parts by mass of nano titanium dioxide, adding 45 parts by mass of polyoxyethylene monomethyl ether methacrylate and 70 parts by mass of 5 vt.% HCl solution, and heating in a water bath at 85 ℃ for 1.5h under the condition of magnetic stirring, wherein the nano titanium dioxide is rutile type nano titanium dioxide, and the particle size is 20-50 nm.
And step two, cooling the mixture to room temperature after heating, then carrying out centrifugal separation at the rotating speed of 600r/min, washing the mixture after centrifugal separation by using deionized water, and drying to obtain the nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate.
And thirdly, taking 4 parts by mass of acrylic acid, 5 parts by mass of calcium lignosulphonate and 85 parts by mass of 75wt.% ethanol, heating to 55 ℃ under the conditions of stirring and nitrogen filling, and reacting for 40 min.
And step four, adding 25 parts by mass of the dried nano titanium dioxide modified polyoxyethylene monomethyl ether methacrylate in the step two and 4 parts by mass of a 5wt.% ammonium persulfate aqueous solution into the reacted mixture, and then heating to 75 ℃ to react for 4 hours.
And step five, after the reaction is finished, neutralizing the reaction product by using a 30wt.% NaOH solution until the pH value is 7, and finally obtaining the modified cement dispersant.
The modified cement dispersants prepared in examples 1 to 3 and comparative example 1 were tested. Referring to the relevant regulations of the national standard GB.T8077-2000 'test method for homogeneity of concrete admixture', the mixing amount of the samples prepared in the embodiments 1-3 and the comparative example 1 is 0.3 wt% of the cement dosage, the fluidity of the net paste on the plate glass is tested after stirring for three minutes, and the fluidity of the net paste after 30 minutes is tested. The results of the experimental tests are referred to in the table below.