Πρόσθετα ελαφρού σκυροδέματος | Αφριστικοί παράγοντες υψηλής απόδοσης για κυψελωτό σκυρόδεμα
Influence mechanism of υπερρευστοποιητής on concrete properties
Ο υπερρευστοποιητής είναι ουσιαστικά ένα είδος οικοδομικών υλικών, στη χρήση αφρού και φυσαλίδων και άλλων φυσαλίδων sol, και έχουν διαφορετικά χαρακτηριστικά και μηχανισμό σχηματισμού, is caused by ionic superplasticizer. After adding superplasticizer in the concrete mixture, superplasticizer will adsorb on the surface of cement particles. Γενικά, για 80% of superplasticizer will be adsorbed by cement particles, so that they can maintain aggregation state for a long time without diffusion. When not adding superplasticizer, concrete will have a certain amount of gas content (για 2%), formed by the size of the bubble is uneven, and the distribution is very uneven. After adding superplasticizer to concrete, η κατανομή των παραμέτρων του σκυροδέματος μπορεί να διατηρήσει καλές ιδιότητες και να βελτιώσει την απόδοση εργασίας του σκυροδέματος, such as the tensile strength of concrete. Εκτός, adding superplasticizer in concrete mixing will help reduce water consumption in concrete mixing. The tiny sol air bubbles generated will help fill the micro-pores in concrete, significantly improve the anti-permeability of concrete, and enhance its chemical anti-corrosion and anti-aging ability. The superplasticizer can be integrated into the free water migration of internal materials, which helps to alleviate the static superplasticizer pressure and enhance the resistance of concrete to a repeated freeze-thaw cycle. Superplasticizer can slow down the hydration reaction speed of cement in the middle and late stage, improve the strength of cement and enhance its anti-expansion performance. Επομένως, κατά την ανάμειξη σκυροδέματος, εκτός από την εξέταση της άμμου, πέτρα, τσιμέντο και άλλα συμβατικά υλικά, appropriate addition of a certain amount of superplasticizer to improve the use of concrete performance.
1) Influence of superplasticizer on the slump of freshly mixed concrete
When analyzing the workability and fluidity of concrete, a very key index is a slump. Όσο μεγαλύτερη είναι η τιμή, the better the fluidity of concrete. Slump loss refers to the difference between the concrete slump measured again after a specific time and its initial slump. Οι παράγοντες που επηρεάζουν περιλαμβάνουν το τσιμέντο, χαρακτηριστικά αδρανών και αναλογία νερού-τσιμέντου, και τα λοιπά. The type of superplasticizer is also a key influencing factor. In the early 30min, naphthalene series superplasticizer had the maximum concrete slump loss, λογοδοσία 60%, followed by melamine series superplasticizer agent (30%) and polycarboxylic acid series superplasticizer (20%), which indicated that polycarboxylic acid series superplasticizer had the best concrete slump protection. From its formation mechanism, department of polycarboxylic acid superplasticizer in concrete material will be adsorbed on the surface of cement, according to the trapezoidal way lets the cement molecular polymer adsorption layer formed by the electrostatic repulsion more dispersive effect, enhance its stability, so concrete adding polycarboxylic acid system after superplasticizer, can significantly reduce the slump loss.
(2) Influence of superplasticizer on compressive strength of freshly mixed concrete.
The strength of concrete composed of different types of superplasticizer has different effects. By applying superplasticizer, can significantly reduce the mixing of concrete mixing water consumption, βελτίωση του βαθμού ενυδάτωσης του τσιμέντου, βελτίωση του σκυροδέματος σε κάθε ηλικία (3 ρε, 7 δ και 28 ρε) ένταση, μπορεί να είναι από τρία αποτελείται από υψηλής απόδοσης υπερρευστοποιητής του σκυροδέματος η αντοχή σε θλίψη ήταν σημαντικά υψηλότερη από αυτή του τυφλού σκυροδέματος θλιπτική αντοχή, 3 ρε, 7 ρε, και 28 d ο ρυθμός αύξησης της θλιπτικής αντοχής είναι τόσο υψηλός όσο 15%, 20%, και 30% αντίστοιχα. Εκτός, the type of concrete with the highest compressive strength in the early stage was the concrete mixed with polyhydroxy acid superplasticizer, and its compressive strength value was also the highest after 28 ημέρες. Ωστόσο, το σκυρόδεμα που αποτελείται από υπερρευστοποιητή σειράς ναφθαλίνης έχει σχετικά χαμηλή αντοχή σε θλίψη στο αρχικό στάδιο, πράγμα που δείχνει ότι η πρώιμη απόδοση αντοχής του είναι σχετικά κακή.
(3) Influence of superplasticizer on the early cracking performance of freshly mixed concrete
Physical and chemical reactions will occur between concrete with admixtures, τσιμέντο, και προσμίξεις. A kind of superplasticizer is in the concrete that some kind of cement place forms relatively small slump, appear in another kind of cement however relatively big slump loss may appear, do not exist so the superplasticizer that has a good effect to any kind of cement. In the actual evaluation of concrete quality, commonly used evaluation indicators mainly include concrete slump and strength, but it is easy to ignore the volume stability of concrete, easy to induce early shrinkage cracks, may accelerate concrete cracking, affect the durability and safety of the building structure. From the factors that affect the early cracking of the concrete, in addition to wind speed and ambient temperature, the type and amount of admixture are also very important factors.
The test shows that the maximum crack width and crack area of concrete formed by melamine-based superplasticizer are the smallest, among which the crack area is only 76% of the corresponding value of polycarboxylic acid superplasticizer and 52% of the corresponding value of naphthalene superplasticizer. The maximum crack width was only about 40% of the corresponding value of polycarboxylic acid and naphthalene superplasticizer. In the early crack cracking time of concrete, the influence of admixture variety is not significant, which is related to admixture composition and other factors.
(4) Influence of superplasticizer on the durability of freshly mixed concrete
Superplasticizer on the durability of concrete has a greater impact, mainly manifested as: (1) the impact of concrete frost thaw resistance. Because of the smaller the water-cement ratio, the better the freeze-thaw resistance of concrete. By adding superplasticizer with air entrapment effect, the freeze-thaw resistance of concrete is significantly improved. The volume of air intake should be controlled at about 2%, και το μέγιστο δεν πρέπει να υπερβαίνει 6%. Αλλιώς, the strength and durability of concrete will be adversely affected.
(2) the influence of concrete impermeability. Water-cement ratio, as the main factor affecting the impermeability of concrete, if its value is greater than 0.55, it will exceed the water consumption of cement hydration and form many bleeding holes in concrete, increasing the permeability of concrete. If the water-cement ratio is too small, the workability of concrete will be affected and the anti-permeability of concrete will be adversely affected.
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