Views: 6 Author: Site Editor Publish Time: 2022-01-22 Origin: Site
At present, the foam used to make foamed concrete can only be used to make foamed concrete when it has enough toughness and stability when it is mixed with slurry and has no adverse effect on the condensation and hardening of cementitious materials. Based on this, through experiments, adding hydroxypropyl methyl cellulose (HPMC), which is a kind of foam stabilizing substance, to improve the performance of recycled micro-powder foamed concrete was studied.
Foam itself quality good bad determines the quality of concrete, especially in the regenerative powder foam concrete, waste concrete after crushing, ball mill powder, made by its own existence many uneven and with particles and pore of edges and corners, compared with the ordinary foam concrete, recycled powder bubbles in the foam concrete under mechanical impact is more severe. Therefore, the better the toughness, small pore size, uniformity and dispersion of the foam in the slurry, the better the quality of the recycled micropowder foamed concrete. However, it is very important to make foams with high toughness, equal pore size and shape. In the process of using foaming agent, foam stabilizer plays a very important role. Most of the foam stabilizer is glue material, which can increase the viscosity of solution and change its fluidity when dissolved in water. When used together with foaming agent, it directly increases the liquid film viscosity of foam, increases the elasticity of bubbles and the surface strength of liquid film. 1 test
1.1 the raw material
(1) Cement: 42.5 ordinary Portland cement.
(2) Recycled fine powder: The abandoned concrete specimens in the laboratory were selected and crushed to particles with a particle size less than 15mm by jaw crusher, and then put into the ball mill for grinding. In this experiment, the micropowder prepared by grinding time of 60min was selected.
(3) Foaming agent:soap foaming agent, neutral light yellow viscous liquid.
(4) Foam stabilizer: hydroxypropyl methyl cellulose (HPMC), industrial building materials grade, powder, easily soluble in water.
(5) Water: drinking water. The main physical properties of cementitious materials .
1.2 Mix ratio design and calculation
1.2.1 Mix design
During the trial, can increase or decrease of renewable powder foam concrete in the content, to adjust the size of the dry density, through forming specimen volume difference size, actual size and design to a rough estimate error degree of design experiment, renewable powder foam concrete fluidity of slurry size control within 180 mm + 20 mm.
1.2.2 Calculation of mix ratio
Each ratio design molding 9 groups of standard blocks (100mmx100mmx100mm), standard
The total volume of the test block V0 =(0.1x0.1x0.1)x27 = 2.7x10-2m3, set the total volume V =
1.2x2.7x10-2 = 3.24x10-2m3, foaming agent dosage M0 =0.9V = 0.9x3.24x10-2 =
2.916x10-2kg, water required for diluting foaming agent is MWO.
2. Experimental results and discussion
By adjusting the dosage of HPMC, the influence of different foam systems on the basic properties of recycled micro-powder foamed concrete was analyzed. The mechanical properties of each specimen were tested.
2.1 Influence of HPMC dosage on foam performance
First, let's look at "thin bubbles" and "thick bubbles". Foam is a dispersion of gas in liquid. Bubbles can be divided into "thin bubble" with more liquid and less gas and "thick bubble" with more liquid and less gas. Due to the existence of a large amount of water bubble, and high fluidity, the foam concrete slurry made is very thin, and the bubble water is more, easy to produce gravity drainage, so the recycled powder foam concrete prepared by low strength, more connected pores, is inferior foam. Gas more liquid less foam, stoma formation is dense, only separated by a thin layer of water film, the accumulation of foam density is relatively thin bubble density, molding out of the regeneration of micro powder foam concrete closed pores, high strength, is high-quality foam.
With the increase of HPMC dosage, the density of foam gradually increased, indicating that the foam is more and more dense, foaming agent foaming multiple roughly before 0.4% has a slightly enhanced effect, more than 0.4% after the inhibition effect, indicating that the viscosity of foaming agent solution increases, affecting the foaming ability. With the increase of HPMC dosage, the foam secretion and settlement distance gradually decrease numerically. Before 0.4%, the rate of decrease is large, and when the rate exceeds 0.4%, the rate decreases, indicating that with the increase of foaming agent solution viscosity, the liquid in bubble liquid film is not easy to discharge or the discharge is very small, and the liquid between bubbles is not easy to flow. The bubble liquid film thickness decreases slowly, the bubble burst time is prolonged, the bubble liquid film surface strength is enhanced, the foam also has a certain degree of elasticity, so as to make the stability of the foam
Has been significantly enhanced. The settlement distance value after 0.4% also reflects that the foam is relatively stable at this time. The foaming machine is difficult to foam at 0.8%, and the foam performance is the best at 0.4%, and the foam density is 59kg/m3 at this time.
2.2 Influence of HPMC content on the quality of recycled micro-powder foamed concrete slurry
With the increase of HPMC content, the consistency of slurry increases. When the content is less than 0.4%, the consistency increases slowly and steadily, and when the content is more than 0.4%, the rate accelerates significantly, indicating that the foam is too dense, less bubble water, and higher foam viscosity. In the process of increasing the dosage, the foam mass in slurry is the best in the range of 0.4% ~ 0.6%, and the foam quality is poor outside this range. When the content is less than 0.4%, the distribution of air pores in the slurry is relatively uniform and shows a steady trend of improvement. When the content exceeds this content, the distribution of air pores shows a significant uneven trend, which may also be due to the excessive density and viscosity of foam and poor fluidity, resulting in the bubbles cannot be evenly dispersed in the slurry during the stirring process.
2.3 Influence of HPMC content on performance of recycled micropowder foamed concrete
No matter how the foam is produced, the size of the bubbles in the foam will never be completely uniform. Test of recycled waste powder after crushing grinding system, its shape is not uniform, smooth in the bubble and the mixed slurry mixing, the irregular shape of slurry with edges and corners, spikes of particles can produce extremely adverse effect of foam, they contact than as a point of contact with the surface, produce stress concentration, stabbing bubble, causing bubbles burst, so, The preparation of recycled micropowder foamed concrete requires higher stability of the foam. Figure 4 shows the influence rule of different foam systems on the performance of recycled micropowder foamed concrete.
Before 0.4%, the dry density gradually decreased and the rate was faster, and the water absorption was improved. After 0.4%, the dry density changes, and the water absorption rate increases suddenly. In 3D, the compressive strength basically has no difference before 0.4%, and the strength value is about 0.9mpa. After 0.4%, the intensity value is small. The compressive strength at 7d has obvious difference. The strength value at the dosage of 0.0 is obviously not as big as that at 0.2% and 0.4%, but higher than that at 0.6% and 0.8%, and the strength value at 0.2% and 0.4% still has little difference. The change of strength value at 28d was basically the same as that at 7d.
Dosage 0.0 basic show thin bubble, bubble toughness, stability is bad, in the process of slurry mixing and specimen condense sclerosis, there is a lot of bubble breakage, the internal porosity of the specimen is higher, after forming specimen performance is poor, with the increase of dosage, its performance gradually getting better, the bubble in the slurry dispersed more evenly and burst to a lesser degree, After molding, there are more closed holes in the internal structure of the specimen, and the shape, aperture and porosity of the holes are better improved, and the performance of the specimen is better. Showed a trend of decrease 0.4%, strength and its value is not high as 0.0, may be because the foam density and viscosity is too large, illiquid cause in the process of mixing slurry, foam cannot mix with cement mortar, the bubble can't be well evenly dispersed in the slurry, which results in the forming of the specimen is the size of the different degree of bubbles, As a result, there are large holes and connected holes in the specimen after solidification and hardening, resulting in poor structure, low strength and high water absorption rate of the internal holes of the specimen. In the figure, the main reason for the strength change is the pore junctions in the inner part of the micropowder foam concrete
The improvement of structure also reflects that HPMC has no adverse effect on the hydration of cement. When HPMC content is roughly in the range of 0.2% ~ 0.4%, the strength of recycled micropowder foamed concrete is better.
Foam is a necessary factor for making foamed concrete, and its quality is directly related to the quality of foamed concrete. In order to ensure sufficient stability of foams, foaming agent and HPMC are mixed to use. From the analysis of foam, slurry and final concrete quality, it is found that:
(1) The addition of HPMC has a good improvement effect on the performance of foam. Compared with 0.0, the foaming agent foaming ratio increased by 1.8 times, foam density increased by 21 kg/m3, 1h bleeding water decreased by 48 mL, 1h settlement distance decreased by 15 mm;
(2) the HPMC added to improve the regeneration of the overall quality of the powder foam concrete slurry, compared to not mix, rationally increasing the slurry consistency, improve the liquidity and improve the stability of the slurry bubble, enhance the uniformity of the foam dispersed in the slurry, reduce the connecting hole, large hole and the emergence of the phenomenon such as collapse mode, dosage of 0.4%, After the molding specimen is cut, its aperture is small, the shape of the hole is more round, the distribution of the hole is more uniform;
(3) When HPMC content is 0.2% ~ 0.4%, the 28d compressive strength of recycled micropowder foamed concrete is higher, but considering dry density, water absorption and early strength, the best is when HPMC content is 0.4%. At this time, dry density 442 kg/m3, 7d compressive strength 2.2mpa, 28d compressive strength 3.0mpa, water absorption 28%. HPMC plays a good role in the performance of recycled micro-powder foamed concrete, which reflects that HPMC has good adaptability and compatibility when used in recycled micro-powder foamed concrete.