Method for preparing recycled aggregate using construction waste

Abstract

The present invention provides a method for producing recycled aggregate from construction waste. This method uses a staged heating process to remove moisture from the waste and alter the structure of the gel components within it, facilitating the crushing and washing of the dried waste. Acid soaking and washing remove the gel components and metal ions from the waste. The washed aggregate is then soaked in a mixture of silicon dioxide and sodium silicate to improve the properties of the recycled aggregate. The resulting recycled aggregate has a water absorption rate of 1.8% and a crushability index of 7.5%.

Description

Technical Field

[0001] The present invention relates to the field of concrete, and in particular to a method for preparing recycled aggregate by utilizing construction waste. Background Art

[0002] Construction waste, also known as construction waste, includes concrete blocks, rubble, brick and tile fragments, and waste mortar generated by construction units during the construction, renovation, expansion, and demolition of various buildings, structures, and pipelines, as well as by residents during the decoration and renovation of their homes. With the development of urbanization, the amount of construction waste discharged from engineering projects has increased year by year, while its recycling and utilization have been slow, resulting in a consistently low utilization rate. Currently, crude landfill disposal occupies a large amount of land resources, not only wasting manpower and material resources on maintaining the discharge site, but also affecting vegetation and groundwater, leading to secondary environmental pollution. Therefore, how to expand the utilization of construction waste, improve its utilization rate, and thereby resolve the land resource and environmental problems caused by the large-scale discharge of construction waste has become a technical issue that the government and environmental protection companies urgently need to address. Summary of the Invention

[0003] In view of this, the present invention proposes a method for preparing recycled aggregate using construction waste to solve the above problems.

[0004] The technical solution of the present invention is achieved as follows:

[0005] A method for preparing recycled aggregate using construction waste comprises the following steps:

[0006] (1) removing the construction waste using a cleaning device to obtain cleaned construction waste;

[0007] (2) drying the construction waste after impurities removal by a secondary drying process to obtain dried construction waste;

[0008] (3) crushing the dried construction waste to obtain crushed aggregate, and washing the crushed aggregate using a water washing process to obtain washed aggregate;

[0009] (4) The washed aggregate is soaked in a mixture of silicon dioxide and sodium silicate and dried to obtain recycled aggregate.

[0010] Furthermore, in step (2), the secondary drying process has a first drying temperature of 150-180° C., a drying time of 50-70 min, and a second drying temperature of 200-230° C., a drying time of 90-120 min.

[0011] Furthermore, in step (2), the heating rate of the first drying temperature in the secondary drying process is 3-5°C / min, and the heating rate of the second drying temperature is 8-10°C / min.

[0012] The secondary drying process used in the present invention is beneficial to the aggregate crushing process, can better control the particle size of the crushed aggregate, and is also beneficial to removing impurities such as gel in the water washing process.

[0013] Furthermore, in step (3), the particle size of the crushed aggregate is 2-3 cm.

[0014] Furthermore, in step (3), the crushed aggregate is washed with water by soaking the crushed aggregate in a hydrochloric acid solution with a concentration of 0.05-0.08 mol / L, the aggregate soaked in the hydrochloric acid solution is rinsed with clean water, and the washed aggregate is mixed with an ion exchange resin and sieved.

[0015] Furthermore, the mass ratio of the washed aggregate, ion exchange resin and water is 100:5-10:100-150, and the mixing is performed by stirring at 70-100 rpm / min for 7-10 minutes and standing for 20-30 minutes.

[0016] In the present invention, the dried aggregate is first treated with a hydrochloric acid solution with a concentration of 0.05-0.08 mol / L and then mixed with an ion exchange resin, which can fully remove gel components, metal ions and powder in construction waste. The water washing process of the present invention can also reduce the alkali content in the aggregate, avoiding the reaction of the alkali in the aggregate with the mixed solution of silicon dioxide and sodium silicate, which causes the performance of the aggregate to deteriorate.

[0017] Furthermore, in step (4), the drying temperature is 120-150° C., and the drying time is 2-4 hours.

[0018] Furthermore, in step (4), the silica and sodium silicate mixture comprises 10-15 wt% of sodium silicate and 5-8 wt% of silica, and the soaking time is 90-120 min.

[0019] The present invention uses aggregate soaked in a mixture of silicon dioxide and sodium silicate to fill a large number of cavities and gaps in the aggregate, modify the surface of the aggregate, improve the mechanical properties of the recycled aggregate, and further improve the use effect of the recycled aggregate.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention discloses a method for preparing recycled aggregate from construction waste. The method removes moisture from the construction waste and changes the structure of the gel components in the construction waste by a staged heating method, which facilitates the crushing or water washing of the dried construction waste. The water washing process removes the gel components and metal ions in the construction waste. Due to the removal of the gel components, metal ions, and powder in the construction waste, the water washing process of the present invention can also reduce the alkali content in the aggregate, preventing the alkali in the aggregate from reacting with a mixture of silica and sodium silicate, which would otherwise degrade the aggregate's performance. The water washing process results in a large number of cavities and gaps in the aggregate. By soaking the aggregate in a mixture of silica and sodium silicate, the aggregate surface is modified, improving the mechanical properties of the recycled aggregate and further enhancing the use effect of the recycled aggregate. DETAILED DESCRIPTION

[0022] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0023] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0024] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0025] The ion exchange resin used in the present invention is amino resin.

[0026] Example 1

[0027] A method for preparing recycled aggregate using construction waste comprises the following steps:

[0028] (1) removing the construction waste using a cleaning device to obtain cleaned construction waste;

[0029] (2) drying the construction waste after impurities removal by a secondary drying process, wherein the first drying process is performed by heating the temperature to 150°C at 3°C / min and drying for 50 minutes, and the second drying process is performed by heating the temperature to 200°C at 8°C / min and drying for 90 minutes, thereby obtaining dried construction waste;

[0030] (3) The dried construction waste is crushed to obtain aggregate with a particle size of 2-3 cm. The crushed aggregate is soaked in a hydrochloric acid solution with a concentration of 0.05 mol / L for 2 h. The aggregate soaked in the hydrochloric acid solution is rinsed with clean water. The rinsed aggregate is mixed with ion exchange resin, stirred at 70 rpm / min for 7 min, and allowed to stand for 20 min. The mass ratio of aggregate, ion exchange resin and water is 100:5:100. The aggregate and ion exchange resin are sieved to obtain washed aggregate;

[0031] (4) The washed aggregate was soaked in a mixture of 10 wt% sodium silicate and 5 wt% silicon dioxide for 90 min and dried at 120° C. for 2 h to obtain recycled aggregate.

[0032] Example 2

[0033] A method for preparing recycled aggregate using construction waste comprises the following steps:

[0034] (1) removing the construction waste using a de-impurity device to obtain de-impurity construction waste;

[0035] (2) drying the construction waste after impurities removal by a secondary drying process, wherein the first drying process is performed by heating the temperature to 180° C. at 5° C. / min and drying for 70 min, and the second drying process is performed by heating the temperature to 230° C. at 10° C. / min and drying for 120 min, thereby obtaining dried construction waste;

[0036] (3) The dried construction waste is crushed to obtain aggregate with a particle size of 2-3 cm. The crushed aggregate is soaked in a hydrochloric acid solution with a concentration of 0.08 mol / L for 4 hours. The aggregate soaked in the hydrochloric acid solution is rinsed with clean water. The rinsed aggregate is mixed with ion exchange resin, stirred at 100 rpm / min for 10 minutes, and allowed to stand for 30 minutes. The mass ratio of aggregate, ion exchange resin and water is 100:10:150, and the aggregate is sieved to obtain washed aggregate;

[0037] (4) The washed aggregate was soaked in a mixture of 15 wt% sodium silicate and 8 wt% silicon dioxide for 120 min and dried at 150° C. for 4 h to obtain recycled aggregate.

[0038] Example 3

[0039] A method for preparing recycled aggregate using construction waste comprises the following steps:

[0040] (1) removing the construction waste using a de-impurity device to obtain de-impurity construction waste;

[0041] (2) drying the construction waste after impurities removal by a secondary drying process, wherein the first drying process is performed by heating the temperature to 170°C at 4°C / min and drying for 60 minutes, and the second drying process is performed by heating the temperature to 20°C at 9°C / min and drying for 115 minutes, thereby obtaining dried construction waste;

[0042] (3) The dried construction waste is crushed to obtain aggregate with a particle size of 2-3 cm. The crushed aggregate is soaked in a hydrochloric acid solution with a concentration of 0.06 mol / L for 3 hours. The aggregate soaked in the hydrochloric acid solution is rinsed with clean water. The rinsed aggregate is mixed with ion exchange resin, stirred at 85 rpm / min for 9 minutes, and allowed to stand for 25 minutes. The mass ratio of aggregate, ion exchange resin and water is 100:8:130, and the aggregate is sieved to obtain washed aggregate;

[0043] (4) The washed aggregate was soaked in a mixture of 13 wt% sodium silicate and 6.5 wt% silicon dioxide for 110 min and dried at 135° C. for 3 h to obtain recycled aggregate.

[0044] Comparative Example 1

[0045] The difference from Example 3 is that the concentration of hydrochloric acid is changed, specifically:

[0046] A method for preparing recycled aggregate using construction waste comprises the following steps:

[0047] (1) removing the construction waste using a de-impurity device to obtain de-impurity construction waste;

[0048] (2) drying the construction waste after impurities removal by a secondary drying process, wherein the first drying process is performed by heating the temperature to 170°C at 4°C / min and drying for 60 minutes, and the second drying process is performed by heating the temperature to 20°C at 9°C / min and drying for 115 minutes, thereby obtaining dried construction waste;

[0049] (3) The dried construction waste is crushed to obtain aggregate with a particle size of 2-3 cm. The crushed aggregate is soaked in a hydrochloric acid solution with a concentration of 1 mol / L for 3 h. The aggregate soaked in the hydrochloric acid solution is rinsed with clean water. The rinsed aggregate is mixed with ion exchange resin, stirred at 85 rpm / min for 9 min, and allowed to stand for 25 min. The mass ratio of aggregate, ion exchange resin and water is 100:8:130, and the aggregate is sieved to obtain washed aggregate;

[0050] (4) The washed aggregate was soaked in a mixture of 13 wt% sodium silicate and 6.5 wt% silicon dioxide for 110 min and dried at 135° C. for 3 h to obtain recycled aggregate.

[0051] Comparative Example 2

[0052] The difference from Example 3 is that the drying process is changed, specifically:

[0053] A method for preparing recycled aggregate using construction waste comprises the following steps:

[0054] (1) removing the construction waste using a de-impurity device to obtain de-impurity construction waste;

[0055] (2) drying the construction waste after impurities removal, heating the waste to 20° C. at 9° C. / min and drying the waste for 115 min to obtain dried construction waste;

[0056] (3) The dried construction waste is crushed to obtain aggregate with a particle size of 2-3 cm. The crushed aggregate is soaked in a hydrochloric acid solution with a concentration of 0.06 mol / L for 3 hours. The aggregate soaked in the hydrochloric acid solution is rinsed with clean water. The rinsed aggregate is mixed with ion exchange resin, stirred at 85 rpm / min for 9 minutes, and allowed to stand for 25 minutes. The mass ratio of aggregate, ion exchange resin and water is 100:8:130, and the aggregate is sieved to obtain washed aggregate;

[0057] (4) The washed aggregate was soaked in a mixture of 13 wt% sodium silicate and 6.5 wt% silicon dioxide for 110 min and dried at 135° C. for 3 h to obtain recycled aggregate.

[0058] Comparative Example 3

[0059] The difference from Example 2 is that no ion exchange resin treatment is used, specifically:

[0060] A method for preparing recycled aggregate using construction waste comprises the following steps:

[0061] (1) removing the construction waste using a de-impurity device to obtain de-impurity construction waste;

[0062] (2) drying the construction waste after impurities removal by a secondary drying process, wherein the first drying process is performed by heating the temperature to 170°C at 4°C / min and drying for 60 minutes, and the second drying process is performed by heating the temperature to 20°C at 9°C / min and drying for 115 minutes, thereby obtaining dried construction waste;

[0063] (3) crushing the dried construction waste to obtain aggregate with a particle size of 2-3 cm, soaking the crushed aggregate in a hydrochloric acid solution with a concentration of 0.06 mol / L for 3 h, and rinsing the aggregate after soaking in the hydrochloric acid solution with clean water to obtain washed aggregate;

[0064] (4) The washed aggregate was soaked in a mixture of 13 wt% sodium silicate and 6.5 wt% silicon dioxide for 110 min and dried at 135° C. for 3 h to obtain recycled aggregate.

[0065] Comparative Example 4

[0066] The difference from Example 3 is that the composition of the mixed solution in step (4) is changed to:

[0067] A method for preparing recycled aggregate using construction waste comprises the following steps:

[0068] (1) removing the construction waste using a de-impurity device to obtain de-impurity construction waste;

[0069] (2) drying the construction waste after impurities removal by a secondary drying process, wherein the first drying process is performed by heating the temperature to 170°C at 4°C / min and drying for 60 minutes, and the second drying process is performed by heating the temperature to 20°C at 9°C / min and drying for 115 minutes, thereby obtaining dried construction waste;

[0070] (3) The dried construction waste is crushed to obtain aggregate with a particle size of 2-3 cm. The crushed aggregate is soaked in a hydrochloric acid solution with a concentration of 0.06 mol / L for 3 hours. The aggregate soaked in the hydrochloric acid solution is rinsed with clean water. The rinsed aggregate is mixed with ion exchange resin, stirred at 85 rpm / min for 9 minutes, and allowed to stand for 25 minutes. The mass ratio of aggregate, ion exchange resin and water is 100:8:130, and the aggregate is sieved to obtain washed aggregate;

[0071] (4) The washed aggregate was soaked in a 10 wt% slag powder solution for 60 min, dried, and then soaked in a 10 wt% polyvinyl alcohol solution for 60 min, and dried at 135° C. for 3 h to obtain recycled aggregate.

[0072] Comparative Example 5

[0073] The difference from Example 3 is that step (4) is not performed, specifically:

[0074] A method for preparing recycled aggregate using construction waste comprises the following steps:

[0075] (1) removing the construction waste using a de-impurity device to obtain de-impurity construction waste;

[0076] (2) drying the construction waste after impurities removal by a secondary drying process, wherein the first drying process is performed by heating the temperature to 170°C at 4°C / min and drying for 60 minutes, and the second drying process is performed by heating the temperature to 20°C at 9°C / min and drying for 115 minutes, thereby obtaining dried construction waste;

[0077] (3) The dried construction waste is crushed to obtain aggregate with a particle size of 2-3 cm. The crushed aggregate is soaked in a hydrochloric acid solution with a concentration of 0.06 mol / L for 3 hours. The aggregate soaked in the hydrochloric acid solution is rinsed with clean water. The rinsed aggregate is mixed with ion exchange resin, stirred at 85 rpm / min for 9 minutes, and allowed to stand for 25 minutes. The mass ratio of aggregate, ion exchange resin and water is 100:8:130, and the aggregate is sieved to obtain washed aggregate.

[0078] Test Example 1

[0079] The water absorption and crushing index of the recycled aggregates prepared in Example 3 and Comparative Examples 1-5 were tested with reference to GB / T25177-2010.

[0080] name Water absorption (%) Crushing index (%) Example 3 1.8 7.5 Comparative Example 1 2.3 8.8 Comparative Example 2 2.1 8.5 Comparative Example 3 2.9 9.7 Comparative Example 4 1.9 8.2 Comparative Example 5 8.9 11.6

[0081] The test results show that the recycled aggregate prepared by the present invention has low water absorption and low crushing index. In Comparative Example 1, the hydrochloric acid concentration is changed and a higher concentration of hydrochloric acid solution is used for soaking. The excessively high concentration not only affects the removal of gel components in the aggregate, but also leads to a decrease in the effect of the ion exchange resin in removing impurities such as gel structure and metal ions. Comparative Example 2 adopts a one-time drying method, which leads to a decrease in the performance of the obtained recycled aggregate. In the present invention, a reasonable drying process is used to separate the gel structure, impurities and aggregate in the waste aggregate, which is beneficial to the removal of gel and, more importantly, to the volatilization of some heavy metal ions in the aggregate. In Comparative Example 3, ion exchange resin is not used, resulting in insufficient removal of impurities in the aggregate. The washed aggregate and the mixed solution of silica and sodium silicate reduce the effect. Comparative Example 4 changes the composition of the mixed solution in step (4) and soaks in a mixed solution of silica and sodium silicate to modify the surface of the aggregate and improve the mechanical properties of the recycled aggregate. In Comparative Example 5, step (4) was omitted. The aggregate after drying and washing contained numerous voids and gaps on its surface and interior. The present invention achieves this by soaking the aggregate in a mixture of silica and sodium silicate, thereby filling and modifying the surface. Furthermore, when the recycled aggregate of the present invention is used as new aggregate, it can be fully integrated into the mortar, improving the performance of the concrete.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing recycled aggregate using construction waste, characterized in that: The following steps are involved: (1) Using a cleaning device to remove construction waste to obtain cleaned construction waste; (2) drying the construction waste after impurities removal using a secondary drying process to obtain dried construction waste; The first drying temperature of the secondary drying process is 150-180°C, the drying time is 50-70min, the second drying temperature is 200-230°C, and the drying time is 90-120min; the first drying temperature of the secondary drying process is increased at a rate of 3-5°C / min, and the second drying temperature is increased at a rate of 8-10°C / min; (3) crushing the dried construction waste to obtain crushed aggregate, and washing the crushed aggregate using a water washing process to obtain washed aggregate; The water washing process comprises soaking the crushed aggregate in a hydrochloric acid solution with a mass concentration of 0.05-0.08 mol / L, rinsing the aggregate soaked in the hydrochloric acid solution with clean water, mixing the rinsed aggregate with an ion exchange resin, and sieving; the mass ratio of the rinsed aggregate, ion exchange resin, and water is 100:5-10:100-150, and the mixing is stirred at 70-100 rpm / min for 7-10 minutes and allowed to stand for 20-30 minutes; (4) Soaking the washed aggregate in a mixture of silica and sodium silicate, and drying it to obtain recycled aggregate; the drying temperature is 120-150° C., and the drying time is 2-4 hours; the silica and sodium silicate mixture includes 10-15wt% sodium silicate and 5-8wt% silica, and the soaking time is 90-120 minutes.

2. The method for preparing recycled aggregate from construction waste according to claim 1, characterized in that: In step (3), the particle size of the crushed aggregate is 2-3 cm.