Effect of Retarder on slump retention of polycarboxylate superplasticizer

Slump loss of concrete has always been a research hotspot. At present, chemical admixtures are mainly used to control slump loss. Polycarboxylate superplasticizer is a kind of concrete superplasticizer with comb shape and adjustable structure, which can be used to prepare all kinds of high performance concrete. The molecular weight, side chain length and the type of adsorption group of Polycarboxylate superplasticizer will affect the retention performance of concrete.

Slump retaining Polycarboxylate superplasticizer mainly introduces ester group into the molecule, stores part of anchoring group, and slowly hydrolyzes to release anchoring group under alkaline condition of cement. The slump loss of concrete is caused by the decrease of superplasticizer concentration in cement paste. The faster the content of superplasticizer decreases, the faster the fluidity loss of cement paste. However, the initial setting time of ordinary portland cement is about 3 hours. In order to maintain it for a long time, it is necessary to explore the synergistic effect between retarder and polycarboxylate superplasticizer.

In this paper, sodium gluconate (SG), citric acid (CA), white sugar (WS) and amino trimethylene phosphate (ATMP) were used to investigate the release law of retarder and slump retaining Polycarboxylate superplasticizer, which laid a foundation for the application of Polycarboxylate superplasticizer.

1 Test part
(1) Test materials
Retarder: sodium gluconate, industrial grade; white granulated sugar, food grade; citric acid monohydrate, food grade; aminotrimethylene phosphonic acid, industrial grade. Superplasticizer: high water reducing polycarboxylate superplasticizer (sdpc-7), self-made, concentration 50%; slump retaining polycarboxylate superplasticizer (sdpc-8), self-made, concentration 50%. Reference cement: specific surface area 340 m2 / kg, 80 μ m sieve residue 0.8%, 3D compressive strength 27.7mpa, 28d compressive strength 49.8mpa. P · o42.5 cement: Beijing Jinyu Beishui ordinary portland cement, with specific surface area of 420 m2 / kg, standard consistency water demand of 28.4%, 80 μ m sieve residue of 1.2%, 3D mortar compressive strength of 29.3mpa, 28d mortar compressive strength of 52.2mpa. Grade II fly ash: 45 μ m sieve residue 16%, water demand ratio 104%, 7d activity index 65%. S95 grade ore powder: 7d activity index 85%, 28d activity index 99%. Sand: reasonable grading, medium sand in zone II, fineness modulus 2.6, mud content 0.6%. Stone: Granite gravel with reasonable gradation and particle size of 5-25 mm.

(2) Test method
Cement setting time test: the test is conducted according to GB / t1346-2011 "test method for water consumption, setting time and stability of cement standard consistency", in which the dosage of retarder is 0.03% of cement quality.

Water requirement test for standard consistency of cement: the test shall be conducted according to GB / t1346-2001 "test method for water requirement, setting time and stability of standard consistency of cement".

Fluidity test of cement paste: according to gb8077-2012 test method for homogeneity of concrete admixtures, the content of slump retaining Polycarboxylate superplasticizer is 0.15% of cement quality, and the content of retarder is 0.03% of cement quality.

Basic performance test of concrete: according to gb8076-2008 "concrete admixtures" test method, the benchmark mix proportion of concrete is m (cement) m (mineral powder) m (fly ash) m (coarse aggregate) m (sand) m (water) = 25065751043786172 (kg).

2. Results and discussion
(1) Influence of different retarders on setting time of reference cement

Fig. 1 Effect of different retarders on setting time of reference cement

Figure 1 shows the effect of different retarders on the setting time of reference cement (0.03%). It can be seen from Figure 1 that the four retarders SG, CA, WS and ATMP have different degrees of retarding effect on the benchmark cement, and the retarding effect is: ATMP > WS >CA> SG. When the dosage is 0.03%, the retarding effect of ATMP is the best in the standard cement system, the initial setting time is 350 min, which is 220 min longer than the blank, the final setting time is 400 min, which is 240 min longer than the blank.

(2) Effect of different retarders on water requirement of standard consistency of cement

Fig. 2 Effect of Retarder on water demand of standard consistency of cement

All retarders have a certain auxiliary water reducing effect, so it is necessary to explore the influence of retarders on the water demand of cement standard consistency, and the results are shown in Figure 2. As can be seen from Figure 2, the addition of retarders will reduce the water demand of standard consistency of cement in varying degrees, and the water demand reduction range of the four retarders is about 26%, which is 1.5% lower than the blank. That is to say, the addition of retarder can assist in water reduction, but the water reduction rate of single addition is low.

(3) Effect of different retarders on fluidity of reference cement paste

Fig. 3 Effect of different retarders on the expansion of reference cement paste

The influence of different retarders on the expansion of reference cement paste is shown in Figure 3. It can be seen from Figure 3 that with the addition of sdpc-8, the expansion degree of the reference cement paste reaches the maximum value of 270 mm in 1 h, which is 130 mm higher than the initial value, and begins to lose after 2 h, and completely loses its fluidity in 5 h. The addition of retarder can prolong the retention time of cement paste in varying degrees, and the extent of prolonging the retention time of cement paste is ATMP > WS > CA > SG. When ATMP content is 0.03% and sdpc-8 content is 0.15%, the retention time of the slurry is the longest, and the expansion of the slurry can still reach 260mm after 5h, which is 120mm higher than the initial. That is to say, the addition of retarder can improve the retention performance of polycarboxylate superplasticizer, but different retarders have different auxiliary retention effects.

(4) Influence of different retarders on concrete performance

Table 1 working performance of concrete prepared with different retarders

The working performance of concrete prepared with different retarders and water reducing agents is shown in Table 1. It can be seen from table 1 that polycarboxylate superplasticizer also has a certain retarding effect, and with the addition of retarder, the setting time of concrete has different degrees of extension, among which the strongest retarding effect is ATMP. When the dosage is 0.03%, the initial setting time is 20 hours and 50 minutes, which is 8 hours and 30 minutes longer than the blank. The results show that the synergistic effect of the retarder and the retarder is not obvious when the dosage of the retarder is 0.03%.

Fig. 4 Effect of different retarders on compressive strength of concrete

Figure 4 shows the change of concrete compressive strength. It can be seen from Figure 4 that the addition of retarder can reduce the concrete strength in different degrees, and the reduction range is ATMP > WS > CA > SG. When the retarder is not added (blank), the 3D compressive strength of concrete is 15MPa, the 7d compressive strength is 28Mpa, and the 28d compressive strength is 45MPa; when 0.03% ATMP is added, the compressive strength of concrete decreases most seriously, the 3D compressive strength is 11mpa, 4MPa lower than the blank, the 7d compressive strength is 23mpa, 5MPa lower than the blank, the 28d compressive strength is 42MPa, 3Mpa lower than the blank.

3. Conclusion

(1) When the dosage of retarder is 0.03%, the retarding effect of cement is ATMP > WS > CA > SG, and ATMP has the best retarding effect. The water requirement of standard consistency of cement is about 26%. When the dosage of sdpc-8 and ATMP is 0.15% and 0.03%, the retention time of the slurry is the longest, and the 5 h expansion reaches 260mm.

(2) In the concrete system, when the content of ATMP is 0.03%, the retarding effect is the strongest, the initial setting time is 20:50 minutes, 8:30 minutes longer than the blank, and the slump of concrete does not lose for 3 hours, the effect of slump preservation is obvious, but the compressive strength of concrete decreases the most seriously.

(3) The results show that the retarder and the slump retaining polycarboxylate superplasticizer have synergistic slump retaining effect, but excessive retarder will prolong the setting time and affect the compressive strength of concrete.

Ps： About PCE

1. Why use Polycarboxylate superplasticizer ? As follows:

1) High early strength: significant increase of early strength and 28d strength
2) Low slump lose: Great reduction of slump lose
3) Excellent durability: Reduction of cracking, shrinkage and creep
4) High water reduction: Water reduction more than 30% according to different application
5) Environmental-friendly products: Non pollution during production
6) Excellent compatibility with various types of cements
7) Low chloride and alkali content, no corrosion to steel-bar

2. Which Product of Polycarboxylate superplasticizer do you need ? Look into them one by one:

Polycarboxylate Superplasticizer (PCE) 50% Liquid

Polycarboxylate Superplasticizer (PCE) Powder

Polycarboxylate Superplasticizer (PCE) Flake/ Granular

Equipment Design for Synthesizing Polycarboxylate Superplasticizer Liquid

1) Polycarboxylate Superplasticizer (PCE) 50% Liquid
SJZ-53C High slump retention
SJZ-41A High water reducing
SJZ-31E high water-reducing and high early-strength

Various types of strength grade ready-mixed concrete
High strength, Ultra high strength concrete
Self-compacting concrete
Various types of pumping concrete, precast concrete, etc.
Low water/cement ratio, High early strength concrete
Various types of concrete of the long-distance transportation

(2) Polycarboxylate Superplasticizer (PCE) Powder
SJZ-018 High water reducing
SJZ-101 High water reducing
SJZ-401 Water reducing+Slump Retention

We supply two types of Polycarboxylate superplasticizer(PCE) powder, one is polyester base (SJZ-018) and the other is polyether base (SJZ-101/401). The product is widely used in dry-mortar and concrete systems, such as high-performance concrete, high flowability concrete, high durability concrete, high strength mortar, gypsum products, self-leveling floor, joint filler, grouts etc.

(3) Polycarboxylate Superplasticizer (PCE) Flake/ Granular
SJZ-20 Mainly to prepare PCE liquid

3.Technology informations
Polycarboxylate Superplasticizer (PCE) is a kind of superplasticizer emerged in the early 80's. It is mainly used in cement concrete. In chemistry, Poly-carboxylate-based is an organic and polymeric electrolyte. It belongs to a polymer surfactant. Therefore, it can also be applied in other paste materials such as gypsum products and ceramic products to reduce water content.
Poly-carboxylate is a weak electrolyte. It can only be fully dissolved in an alkaline solution. It can compound with cations in cement/water system to control the cement hydration process and thus to reduce the slump loss of the concrete. Poly-carboxylate achieves its water reducing effect through the yield of electrostatic repulsion and steric hindrance when it is absorbed to the cement particles. Hence, Poly-carboxylate is the most effective superplasticizer for cement concrete.
Poly-carboxylate is a raw material for superplasticizer. It is recommended that applicants should determine the Poly-carboxylate dosage in their own formulation according to their trial runs.

4.Equipment Design for Synthesizing Polycarboxylate Superplasticizer Liquid

Type: SURE-5T5H
Batch Production: 5Tonnes (MT) per 5Hours
Installation Area: 6m(L)*3m(W)*4.5m(H)
Recommended Workshop Area: 200㎡ or more, with the clear height of  6m(Min).

List of Components for SURE-5T5H:

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