Mechanism Ntawm Kev Ua Ntawm Polycarboxylate Molecules

1.Dispersing Action

Thaum cov cement sib xyaw nrog dej, cov khoom sib xyaw ua ke, tsim cov qauv flocculated uas tuaj yeem ntim 10% -30% ntawm cov dej ntawm cov cement particles. Cov dej khib nyiab no tsis tuaj yeem txav mus los ywj pheej lossis muab lubrication, cuam tshuam rau cov kua dej ntawm cov cement paste. Polycarboxylate molecules adsorb rau saum npoo ntawm cov cement hais, imparting tus nqi tsis zoo uas tsim electrostatic repulsion. Qhov kev txiav txim no txhawb kev tawg ntawm cov cement hais, cuam tshuam cov qauv flocculated thiab tso cov dej ntws los koom rau hauv cov dej ntws. Qhov no piav qhia txog cov dej-txo cov nyhuv ntawm polycarboxylate superplasticizers; lawv txhim kho kev siv dej yam tsis muaj kev txiav txim siab nce lossis txo cov ntsiab lus dej tag nrho. Tsis tas li ntawd, kev tsim cov complexes ntawm COO²⁻ thiab Ca²⁺ ions txo cov concentration ntawm calcium ions nyob rau hauv cov cement paste, ncua lub crystallization ntawm Ca(OH)₂ thiab txo qhov tsim ntawm CSH gel, yog li slowing lub hydration txheej txheem ntawm cov cement. Yog li ntawd, polycarboxylate molecules kuj pom muaj qee qhov kev cuam tshuam ntawm kev cuam tshuam. Interestingly, txoj kev loj hlob ntawm lub zog thaum ntxov-lub zog polycarboxylate daws tej zaum yuav nyuaj vim lawv cov yam ntxwv retarding. Feem ntau cov khoom muaj zog thaum ntxov muaj nyob rau hauv kev ua lag luam vam khom nrog cov neeg ua haujlwm zoo li sodium nitrite thiab triethanolamine kom ua tiav cov txiaj ntsig no.

2.Lubricating Action

Lub sab chains ntawm polycarboxylate superplasticizers muaj hydroxyl thiab ether pawg (-COCC) uas nthuav tawm hydrophilicity. Cov pab pawg no tsim cov ntawv cog lus hydrogen nrog cov dej molecules, tsim cov yeeb yaj kiab dej ntawm qhov chaw ntawm cov cement. Cov yeeb yaj kiab dej no muaj cov khoom siv lubricating zoo, txo qhov kev tiv thaiv ntawm cov cement hais thiab ua kom cov dej ntws ntawm cov pob zeb.

3.Steric Hindrance Effect

Cov ceg ntoo ntawm polycarboxylate superplasticizers muaj kev teeb tsa spatial ntawm qib microscopic. Zoo ib yam li "me me chubby" ua yeeb yam hauv cov yeeb yaj kiab, uas nws cov plaub hau curled tiv thaiv kev sib cuag nrog "loj chubby" cement hais tom qab nws, qhov ze ntawm cov cement hais rau ib leeg, ntau dua qhov cuam tshuam steric hindrance.

Cov nyhuv no txhim kho qhov slump tuav ntawm cov pob zeb. Qhov luaj li cas ntawm cov cement yog nyob rau hauv micrometer ntau yam, thaum polycarboxylate molecules nyob rau hauv nanometer ntau yam, kwv yees li peb txiav txim ntawm qhov loj me me. Ib qho cement particle tuaj yeem adsorb ntau polycarboxylate molecules. Lub schematic sawv cev ntawm polycarboxylate molecule zoo li lub zuag. Thaum pib, tus cwj pwm "me me chubby" xaus rau hauv qhov xwm txheej txaus ntshai, tsis tuaj yeem txav tawm ntawm cov leeg nqaij "loj chubby," uas thaum kawg qw thiab kov yeej nws. Thaum polycarboxylate molecules ncua cov txheej txheem hydration los ntawm adsorbing mus rau cov cement hais, lawv yuav nws thiaj li tau ntim los ntawm cov khoom hydration, poob lawv cov txiaj ntsig. Zuag qhia tag nrho, qhov adsorption kev txiav txim ntawm polycarboxylate molecules tsis hloov cov khoom ntawm cov cement; nws tsuas yog hloov tus cwj pwm ntws ntawm cov pob zeb tsis cuam tshuam nws lub zog tom qab.