TWI444448B - Preparation of Novel Amphoteric Hydrogels and Its Method as a Self - curing Agent for Concrete - Google Patents

Description

Preparation of novel amphoteric water gel and method thereof as concrete self-curing agent

The invention relates to an amphoteric hydrogel having the structural formula (1). The addition of the water gel in the cement mortar can reduce the moisture weight loss of the cement mortar and maintain a high internal humidity, and is used as a self-supporting concrete with superior performance. Agent.

Concrete is the most widely used civil material for structural construction. The strength of concrete is derived from the hydration of cement, and the hydration of cement can only be carried out in the presence of moisture. If it is in a dry environment, the moisture in the concrete will be volatilized from its surface, so that the hydration of the cement will slow down or even stop with the gradual evaporation of the water, which will cause the concrete to shrink and crack. The purpose of conservation is to keep the concrete with sufficient moisture to ensure that the cement hydration proceeds, develop sufficient strength, and avoid dry shrinkage cracking. The appropriateness of curing will affect the degree of hydration and shrinkage cracking of cement in concrete, which in turn affects the development of strength, durability and volume stability of concrete. If it is not properly maintained, it will not only have an adverse effect on the strength of the concrete, but also tend to produce dry shrinkage cracks, which will make the durability of the concrete structure worse.

The maintenance of high performance concrete is more important than ordinary concrete. In high-performance concrete, due to the chemical admixture, especially the addition of strong plasticizer, the water consumption is lower than that of ordinary concrete, but it still has good workability; and the structure after hard solidification is dense, and the external water is difficult to penetrate. However, compared with general concrete, since the mixing water of high-performance concrete is relatively small, it is more careful to maintain, and if it is not properly maintained, it is more likely to cause shrinkage and affect strength development.

Concrete is usually cured after the pouring operation is completed. The maintenance methods commonly used at construction sites include the stagnant water method and the continuous sprinkling method. These methods are external curing methods, which require periodic watering, watering, or spraying, etc., not only for maintenance and labor, but also for Humidity and dryness often cause cracks inside the structure. Other conservation methods include coverage, demolition, and liquid film maintenance, which are limited in certain work environments or time schedules. Next, it also has its shortcomings and inconvenience. In order to improve these shortcomings, in recent years, some research has turned to the development and application of the "internal curing" method, which is to find a curing agent with water retention/release properties, and add it to concrete to achieve self-maintenance instead. The above method of external curing.

"internal curing agent" or "self-curing agent" is generally a water-soluble resin, a water-absorbent resin or a hydrogel. When added to concrete, it passes through different mechanisms. To make the interior of the concrete retain more water and maintain higher humidity, so that the cement is more hydrated, and the concrete is less prone to cracks due to shrinkage, forming a "self-curing concrete".

Some studies have pointed out that adding water-soluble resin such as polyvinyl alcohol to cementitious materials such as cement slurry, cement mortar or concrete, when the water around the water-soluble resin is volatilized, the resin will precipitate and block the capillary pores of the cementitious material, hindering The loss of moisture, so that more moisture can be retained inside the material, making the cement hydrate more complete. Cement in concrete, mainly C ₃ S (tricalcium citrate), C ₂ S (dicalcium citrate), C ₃ A (tricalcium aluminate) and C ₄ AF (tetracalcium aluminate) In the composition, when the cement encounters water, it will release various ions into the water and react to form hydration products. Therefore, the pore solution in the concrete will contain Na ⁺ , K ⁺ and Ca ² within a few hours. Salts of various ions such as ⁺ , OH ^- and SO ₄ ^2- . In contrast, a water-absorbent resin such as sodium polyacrylate or polyacrylate water gel is added to the cementitious material. Since the water gel can bind moisture inside, it can play the role of a reservoir, and the water in the cementitious material volatilizes. When it is lost to the outside, the water inside the water gel will be released and replenished, so that the material can retain more water and higher humidity, make the cement hydrate more complete, and the material is less likely to shrink and crack.

Compared with the traditional external curing methods, if the internal curing method is adopted, the self-curing agent will be added to the concrete, so that the material itself can be self-maintained, which not only saves man-hours, but also is not restricted by the working environment or time schedule; It can effectively reduce the occurrence of concrete cracks, improve the durability of concrete, reduce the maintenance of concrete structures, and ensure the service life.

Water glue is added to the concrete as a self-supporting agent, mainly as a reservoir. When the interior of the concrete consumes moisture due to the cement hydration reaction, or the water volatilizes from the interior of the concrete to the outside, the water gel can release moisture in a timely manner to keep the interior of the concrete moist and avoid dry shrinkage cracks. Therefore, as a concrete self-curing agent, the water glue not only has a high water absorption rate in pure water, but also has a high water absorption rate in the brine, so that the function of the reservoir can be exerted. Common sodium polyacrylate or polyacrylate water gel can be used as a self-reinforcing agent for concrete, but it has a lot of room for improvement. The reason is that although the water absorption rate of sodium polyacrylate or polyacrylate water gel in pure water is very high, water absorption per gram can reach hundreds or even several kilograms; but the water absorption rate in salt water is very low, usually per gram. Water gel can absorb less than 10 grams of 0.1M CaCl ₂ brine.

The present invention is an amphoteric hydrogel labeled with a network structure having the following formula (1):

Wherein R ₂ and R ₃ are each H or an alkali metal, and m and n are each an integer of from 10 to 1,000. The object of the present invention is to synthesize an amphoteric water gel, which is added to a cementitious material such as cement slurry, cement mortar or concrete, which can reduce the durability of the material due to the occurrence of shrinkage or cracks. Can be used as a concrete curing agent. The amphoteric hydrocolloid is reacted with maleic anhydride and N,N-dimethyl-1,3-propanediamine to give DAPA (4-(3-(bismethylamino)propylamino)-4-carbonyl- 4-(3-(dimethylamino)propylamino)-4-oxo-but-2-enoic acid); DAPA and sodium chloroacetate are reacted to give CDP (4-(3-((carboxymethyl))) Disodium mono(4-(3-((carboxylatomethyl)dimethylammonio)propylamino)-4 -oxobut-2-enoate)) Monomer; finally, the CDP monomer and acrylamide are polymerized to form an amphoteric hydrocolloid. The test results show that the amphoteric hydrogel of the present invention has good water absorption capacity for pure water or salt water; when the moisture inside the cementitious material such as cement slurry, cement mortar or concrete is consumed due to reaction with cement When the volatilization is lost to the outside of the material, the water in the amphoteric hydrogel will slowly be released from the inside to replenish. The addition of the amphiphilic water gel of the invention in the cement mortar can reduce the moisture weight loss of the cement mortar sample and has the water retention effect; adding the amphiphilic water gel of the invention to the cement mortar can also increase the compressive strength of the cement mortar sample. More importantly, the addition of the amphoteric hydrogel of the present invention to the cementitious material can reduce cracks caused by shrinkage of the material and improve the durability of the material. Therefore, the amphiphilic water gel of the invention is a concrete self-curing agent with superior performance.

Amphoteric water gel has the following general formula:

Wherein R ₂ and R ₃ are each H or an alkali metal, and m and n are each an integer of from 10 to 1,000. The synthesis method of the amphoteric hydrocolloid can be illustrated by the following examples.

Embodiment 1

49 grams of maleic anhydride was dissolved in 200 grams of acetone and placed in a four-necked reaction flask. Under an ice bath, 51 g of N,N-dimethyl-1,3-propanediamine was added dropwise, and the reaction was continued for 6 hours under nitrogen. Extracted with acetone 85 g of pink powder DAPA ((4-(3-(dimethylamino)propylamino)-4-oxobut-2-enoic acid)) was obtained. Take 80 g of DAPA and 46.6 g of sodium chloroacetate dissolved in 240 ml of water, place in a four-neck reaction flask, adjust the pH of the solution to 9-10 with sodium hydroxide, and react at 78 ° C for 6 hours. After stirring the reaction at normal temperature for 1 day, it was extracted with acetone to obtain 103 g of CDP monomer.

Take 10 grams of CDP and 3.6 grams of Acrylamide, dissolve in 40 milliliters of deionized water, place in a four-neck reactor, slowly raise the reaction temperature to 75 ° C, then add the appropriate amount of initiator - ammonium persulfate and a crosslinking agent (N, N-methylene-bisacrylamide), and the reaction was continued for 20 minutes until the solution became a colloidal state. The product was immersed in deionized water and replaced with water once a day to remove unreacted monomers. After 3 days, it was taken out and dried in an oven at 55 ° C for 24 hours to obtain 5.5 g of a yellow solid amphoteric hydrocolloid.

The IR spectrum of the amphoteric hydrogel is shown in Figure 1. The absorption peak of NH at wave number 3354 cm ^-1 , the absorption peak of CH at 2931 cm ^-1 , the absorption peak of C=O at 1673 cm ^-1 , 1452 cm ^{- 1} is -NH absorption peak at _2, CN at 1412cm ^-1 to the absorption peak at 1197cm ^-1 absorption peak of CO.

Embodiment 2

Two types of water gel were taken: one was the amphoteric water gel mentioned in the first example, and the other was a polyacrylate water gel (code 283HA from Taiwan Plastics Co., Ltd.). Take appropriate amount of 283HA water gel and amphoteric water gel, put them into tea bag and dip them in deionized water or 0.1M CaCl ₂ brine, soak them for a certain period of time, take out the weight to get the weight of water gel absorbed by water, from water glue The water absorption rate of the water gel can be obtained by the difference in weight before and after water absorption.

The water absorption of two kinds of water gel in deionized water and 0.1M CaCl ₂ brine is shown in Figure 2. It is known from the figure that the water absorption of the water gel increases first with the increase of the soaking time, and then gradually becomes flat, which is the largest. The value is the saturated water absorption. 283HA gel per gram of water saturated water absorption in deionised water and brine 0.1M CaCl ₂ and 586, respectively, 7.2 g; amphoteric water per gram of gel saturated water absorption in deionised water and 0.1M CaCl ₂ brine respectively For 411 and 40 grams. Although the water absorption rate of the amphiphilic water gel is not as good as that of the 283HA water gel, the water absorption rate in the 0.1M CaCl ₂ brine is higher than that of the 283HA water gel because the amphoteric hydrogel has a cation at the same time (-N ⁺ And a functional group of an anion (-COO ^- ).

Embodiment 3

A cement slurry having a water-cement ratio (W/C) of 0.485 was mixed, and a pore solution in the cement slurry was obtained by suction filtration. Then take an appropriate amount of 283HA and amphoteric hydrogel, respectively, after being saturated in deionized water, and then immersed in a pore solution of cement mortar with a water-cement ratio of 0.485 for different time, take out the scale water. Glue weight. During the immersion of the water gel in the aqueous pore solution, the moisture inside the water gel is released to the outside due to the difference in the concentration of ions inside and outside the water gel. The weight of the original water-absorbing saturated water gel is w1, and the weight of the water gel after immersing in the pore water solution for a period of time is w2, then the water retention rate is w2/w1×100%.

Water release rate = 1 - water retention rate

The water retention rate of the two kinds of water gel in the pore water solution is shown in Figure 3. It can be seen from the figure that after the 283HA water gel is placed in the pore water solution, the water will be released quickly due to the poor penetration of the ion concentration in the water gel and the solution. A set value is reached. Each gram of 283HA water gel that absorbs saturated water contains 586 grams of water. After being placed in the pore water solution, the water gel will release water. After 2 hours, each gram of water gel contains 586 grams of water from the initial, and is reduced to contain 11 grams, that is, the water retention rate of 283HA water gel is reduced to 2%, or the water release rate is as high as 98%. In contrast, the water release behavior of amphoteric hydrogel in aqueous pores is quite different from that of 283HA water gel. Each gram of amphoteric hydrocolloid that absorbs saturated water contains 411 grams of water. After being placed in the aqueous solution of pores for 2 hours, the water gel contains 411 grams of water per gram of water gel, which is reduced to 170 grams, which is amphoteric. The water retention rate was reduced to 42%, or the water release rate was 58%, which was much lower than that of 283HA water gel, and then the amphoteric water gel changed from the water release state to the water absorption state. The reason is that the amphiphilic hydrogel changes its functional group after a period of time in the aqueous pore solution, that is, some of the guanamine groups (-CONH ₂ ) in the hydrogel structure are converted into carboxylic acid groups (-COO ^- ), so that the water gel It shows the phenomenon of first releasing water and then absorbing water. This result shows that, compared with 283HA water gel, amphoteric hydrogel is added to cementitious materials such as cement slurry, cement mortar or concrete, which can bind more water inside and play a role as a reservoir. When the moisture in the cementitious material is lost, the water inside the water gel can be released and replenished, so that the cementitious material can retain more water and higher humidity, and the cementitious material is less likely to shrink and crack. .

Embodiment 4

The cement mortar with water-cement ratio (W/C)=0.485 was mixed, and the amphoteric hydrogel dose was added from 0% to 0.25% (% by weight relative to the cement) to prepare a sample of ⁵ × ⁵ × ⁵ cm ³ . At room temperature, the weight of the mortar sample is weighed at regular intervals, and the weight loss of the test body relative to the initial test body (% by weight relative to the cement) can be obtained, which is the weight of the moisture loss in the test body. . Table 1 shows the composition of the amphoteric glue mortar (W/C = 0.485). The cement used is from Portland Cement Company's Type I cement. The fine sand used is Ottawa sand, cement/sand = 1/2.75 (weight ratio), and the right amount of plasticizer A30 is added. (from Qixin Company) to control the fresh mortar to a certain degree of fluidity. The fluidity test of the cement mortar sample is based on CNS1012. After the mixed cement mortar is poured into the mold, it is shaken up and down 25 times in 15 seconds on the flow table, and the spread diameter is measured in 4 times. Take the average.

Figure 4 shows the moisture weight loss of mortar samples with different amphiphilic hydrogel doses. The results show that the weight loss of the test body increases as the standing time increases, and then tends to a fixed value. Add 0.75 grams (water Glue/cement = 0.1%) Amphiphilic hydrogel mortar (M1) and 1.875 g (water gel/cement = 0.25%) amphoteric colloidal mortar (M2) have lower moisture weight loss than unadded Water gel test body (M0). After 28 days of standing, the moisture weight loss of the mortar without the hydrocolloid was 15.7 g, and the moisture weight loss of the mortar with 0.1% and 0.25% amphoteric colloid was 14.5 g and 13.2 g, respectively. Adding water gel mortar to the sample weight loss of 93% and 84%. Therefore, the novel amphoteric water gel of the present invention can reduce the loss of moisture in the cement mortar.

Embodiment 5

The cement mortar having the water-cement ratio (W/C) = 0.485 as in Example 4 was mixed, and the composition thereof is shown in Table 1. The amount of the amphoteric hydrogel added thereto is 0-0.25% (% by weight relative to the cement). The test piece was made into 5x5x5cm ³ and was placed in a constant temperature and humidity chamber with a temperature of 25 ° C and a relative humidity (RH) of 60%. According to CNS1010, the age test period of 3, 7, and 28 days was tested with a compression tester. The compressive strength is taken as the average of the three test tests.

Figure 5 shows the compressive strength of cement mortar samples with different proportions of amphoteric hydrogel. The results show that the compressive strength of the test body first rises first as the curing time increases, and then tends to a fixed value. The compressive strength of the mortar (M1, M2) added with the amphoteric water gel was higher than that of the mortar without the water gel (M0); the mortar sample of 1.875 g (water gel/cement = 0.25%) was added. The compressive strength of (M2) was higher than that of the mortar sample (M1) in which 0.75 g (water gel/cement = 0.1%) of amphoteric colloid was added. After 28 days of standing, the compressive strength of the mortar sample to which no water gel was added was 33.6 MPa, and the compressive strength of the mortar sample to which 0.1% and 0.25% amphoteric water gel was added was 35.2 and 37.8 MPa, respectively. Therefore, the novel amphoteric water gel of the present invention can increase the compressive strength of the cement mortar.

Embodiment 6

The cement mortar with the water-cement ratio (W/C)=0.485 as in the fourth embodiment was mixed into a mold of 2.5×2.5×28.5 cm ³ , and the composition thereof was as shown in Table 1. The dose of the amphoteric hydrogel added was 0. -0.25% (% by weight relative to cement). According to CNS11056, pour the cement mortar into the mold and smear it with a spatula. Place it in a constant temperature and humidity chamber (25°C, 90% RH) for 1 day, then remove the mold and put it into the constant temperature and humidity chamber. °C, 90% RH). Based on the first day, the amount of dry shrinkage of the mortar sample was measured for the next day.

Figure 6 shows the effect of the amphiphilic hydrogel dose on the shrinkage of the cement mortar. The results showed that the dry shrinkage of the test piece first increased with the increase of the standing time, and then tended to be gentle. Adding 0.75 g (water gel/cement = 0.1%) amphoteric colloidal mortar sample (M1) and adding 1.875 g (water gel/cement = 0.25%) amphoteric colloidal mortar sample (M2) It is lower than the mortar sample (M0) to which the amphoteric glue is not added. After 28 days, the dry shrinkage of the mortar without the addition of water gel was 0.214 mm, and the dry shrinkage of the mortar with 0.1% and 0.25% amphoteric colloid was 0.211 and 0.193 mm, respectively, which were lower than those of the mortar. The dry shrinkage of the water gel mortar test body. Therefore, the novel amphoteric water gel of the invention can reduce the dry shrinkage of the cement mortar sample.

Example 7

Mix the cement mortar with the water-cement ratio (W/C)=0.485 as in Example 4 and fill it into the mold. The composition is shown in Table 1. The dosage of the amphoteric hydrogel added is 0-0.25% (relative to cement). Percentage by weight). Mold 5x5x5cm ³ . Pour the cement mortar into the mold and smear it with a spatula. Place it in a constant temperature and humidity chamber (25 ° C, 90% RH) for 1 day, then remove the mold and put it into a constant temperature and humidity chamber (25 ° C, 90). % RH). Based on the first day, the relative humidity of the mortar samples at different times was measured by humidity.

Figure 7 shows the effect of the amphiphilic hydrogel dose on the relative humidity inside the cement mortar. The results show that the relative humidity inside the sample is first fixed (=100% RH), and the humidity starts to decrease with time after a certain time. The relative humidity inside the mortar sample (M1) with 0.75 g (water gel/cement = 0.1%) amphoteric colloidal mortar (M1) and 1.875 g (water gel/cement = 0.25%) amphoteric colloid was added. After 9 days, it began to decrease with time. The mortar sample (M0) without added amphoteric glue began to decrease with time after 8 days. After 28 days, the relative humidity drop inside the mortar without added water gel was 61%, and the mortar with 0.1% and 0.25% amphoteric glue was added. The relative humidity of the parts was 68% and 75%, respectively, which were higher than the internal humidity of the mortar without the addition of water gel. Therefore, the novel amphoteric water gel of the present invention can improve the internal humidity of the cement mortar, thereby reducing the dry shrinkage of the cement mortar sample.

Example eight

A certain amount of cement, water, and 283HA or amphoteric hydrogel were mixed to obtain a cement slurry having a water-cement ratio (W/C) = 0.3, and the composition thereof is shown in Table 2. The amount of hydrogel added therein is 0-0.4% (% by weight relative to cement). The mixed cement slurry was poured into a ring-shaped mold, and the inner ring and the outer ring of the mold were respectively 15 cm, 30 cm in diameter and 2.5 cm in height. There are ribs on the outer ring of the inner ring and the inner surface of the outer ring to promote cracks when the cement slurry test body shrinks. There is a blowing device (air funnel) 8cm above the cement slurry test piece, the wind speed is 4.5m / s, placed on the experimental table at room temperature, after 1 day, observe and record the number of cracks on the surface of the cement slurry test piece, use The following formula calculates the crack index, CI.

CI=(ΣL1+ΣL2)/2

Where L1 = width at the beginning of each crack and L2 = width at the end of each crack.

Cement material such as cement slurry, cement mortar or concrete after pouring, if the surface water volatilization rate is higher than the external or self-replenishing speed, it will shrink and crack. Generally, the higher the cement content in the material and the lower the water content, the more likely cracks are generated. Figure 8 shows the annular water of each group. The mud test specimens were cracked on the surface after a certain period of time under certain conditions (wind speed of 4.5 m/s, room temperature). It can be observed that the addition of water glue is added to the cement slurry to reduce the crack. The CI value of the cement slurry (C0) without added water glue is 0.54 mm, and the CI value of the cement slurry (C3) with 0.1% 283HA water gel is 0.36 mm. The CI value of the cement slurry (C4) to which 0.4% 283A water gel was added was reduced to 0.09 mm. It is shown that adding 283HA water glue to the cement slurry can reduce the crack generation of the cement slurry, and the more the water glue is added, the better the effect. The CI value of the cement slurry (C1) with 0.1% amphoteric hydrogel was 0.15 mm, and the CI value of the cement slurry (C2) with 0.25% amphoteric water gel tends to be 0 mm, confirming that the addition of amphoteric water-gel is more than adding 283HA water-gel. In the cement slurry, the cracking of the cement slurry can be more effectively reduced. The reason is that the amphoteric water-gel is better than the 283HA water gel, and has better water absorption and water retention rate in the pore solution or saline solution in the cement slurry, and can play the role of a reservoir, and tightly binds the water to the water. In cementitious materials. When the moisture in the cementitious material is volatilized, more water inside the amphoteric water gel can be released and replenished, so that the material can retain more water and higher humidity, and the material is less likely to shrink and crack. Therefore, the amphiphilic water gel of the invention is a concrete self-curing agent with superior performance.

Figure 1 IR spectrum of amphoteric hydrogel

Figure 2 Water absorption of amphoteric hydrogel in aqueous solution

Figure 3: Water retention rate of amphoteric hydrogel in pore water solution of cement slurry

Fig.4 Effect of amphiphilic hydrogel dosage on moisture loss of cement mortar

Fig.5 Effect of amphiphilic hydrogel dosage on compressive strength of cement mortar

Figure 6. Effect of amphiphilic hydrogel dosage on dry shrinkage of cement mortar

Figure 7. Effect of amphipathic hydrogel dosage on internal humidity of cement mortar

Figure 8. Crack appearance of the surface of the annular cement paste

Claims (11)

An amphiphilic water gel of the following formula (1): Wherein R ₂ and R ₃ are each H or an alkali metal, and m and n are each an integer of from 10 to 1,000. A method for producing an amphoteric hydrogel as described in claim 1, comprising a ratio of maleic anhydride and N,N-dimethyl-1,3-propanediamine in a ratio of 49:51. The reaction was continued for 6 hours under nitrogen, and 85 parts of DAPA (4-(3-(bismethylamino)propylamino)-4-carbonyl-2-butenoic acid) was extracted with acetone (4-( 3-(dimethyl-amino)propylamino)-4-oxobut-2-enoic acid); DAPA and sodium chloroacetate are contained in 240 parts of water in an amount of 80:46.6, and at pH 9-10, 78 °C The reaction was carried out for 6 hours, and the mixture was stirred at normal temperature for 1 day to obtain CDP (4-(3-((carboxymethyl)) dimethylammonium)propylamino)-4-carbonyl-2-butenoate) ( Disodium mono(4-(3-((carboxylatomethyl)dimethylammonio)propylamino)-4-oxobut-2-enoate)) monomer; finally CDP monomer and acrylamide dissolved in 40 parts by weight in a ratio of 10:3.6 In ionic water, the initiator, ammonium persulfate and the crosslinking agent (N, N-methylene-bisacrylamide), were added dropwise at 75 ° C for 20 minutes. The amphiphilic water gel is formed until the solution undergoes a polymerization reaction in a colloidal state. A method for adding amphoteric hydrogel as described in claim 1 for use as a concrete self-curing agent, which is to add amphoteric hydrogel to a cementitious material such as cement slurry, cement mortar or concrete, as a concrete internal curing Agent. Adding amphoteric hydrogel as described in item 3 of the patent application as a concrete self-curing agent The method wherein the addition of the amphoteric hydrocolloid is between 0.05 and 0.5 wt% (relative to the weight percent of the cement). The method of adding the amphoteric hydrogel as the concrete self-curing agent according to the third application of the patent scope, the water absorption rate per gram of the water gel in water is 300 to 500 grams. The method of adding the amphoteric hydrogel as the concrete self-curing agent as described in claim 3, the water absorption per gram of the water gel in the 0.1 M CaCl ₂ brine is 30 to 50 g. If the amphoteric hydrogel is added as a concrete self-curing agent as described in the third paragraph of the patent application, adding it to the cement mortar can reduce the moisture weight loss of the mortar. The addition of amphoteric hydrogel as a concrete self-curing agent as described in claim 3 of the patent application can be added to the cement mortar to increase the compressive strength of the mortar. If the amphoteric hydrogel is added as a concrete self-curing agent as described in the third paragraph of the patent application, adding it to the cement mortar can reduce the dry shrinkage of the mortar. The addition of amphoteric hydrogel as a concrete self-curing agent as described in claim 3 of the patent application can be added to the cement mortar to increase the humidity inside the mortar. The addition of amphoteric hydrogel as a concrete self-curing agent as described in claim 3 of the patent application can be added to a cementitious material such as cement slurry, cement mortar or concrete to reduce cracking of the material.