Abstract

Objective Monomer in-situ polymerization has emerged as a promising strategy to enhance the toughness of cement-based materials. Unlike conventional polymer toughening methods， which often involve the direct incorporation of pre-formed polymers， in-situ polymerization allows organic monomers to be uniformly dispersed within the cement paste before polymerization. This approach facilitates a more homogeneous distribution and enables the formation of an integrated organic-inorganic composite structure， improving interfacial bonding between the polymer phase and cement hydration products. Consequently， the toughness and deformation capacity of the cement matrix can be significantly enhanced. However， a major challenge persists： the presence of carboxyl groups in certain monomers tends to chelate with calcium ions （Ca²⁺） in the cementitious system， which can disrupt the hydration process and weaken the microstructure， ultimately reducing compressive strength. To date， limited research has been conducted on optimizing monomer selection and polymerization kinetics to mitigate these negative effects while maintaining or even improving mechanical performance. In this study， acrylamide （AM） and N，N-dimethylacrylamide （DMAA） are selected as reactive monomers for in-situ polymerization within the cement matrix. By systematically varying parameters such as total monomer content， AM to DMAA ratio， crosslinking agent （N，N'-methylenebisacrylamide， MBA） concentration， and initiator （ammonium persulfate， APS） dosage， the polymerization process was controlled to tailor the microstructure of the resulting composite. The methodology and findings provide practical insights for enhancing the compressive strength and toughness of cement paste through in-situ polymer modification.

Methods In this work， a series of experiments was designed to fabricate and characterize monomer-modified cement composites. The monomer polymer solution was prepared by dissolving predetermined amounts of AM and DMAA in deionized water under continuous magnetic stirring until a clear and homogeneous solution was obtained. Cement powder was then blended with the aqueous monomer solution using a high-shear mechanical stirrer to ensure uniform dispersion of monomers throughout the paste. The mixture was cast into standard molds and cured at 60°C for different durations （1， 3， and 7 d） to simulate down hole conditions and promote in-situ polymerization concurrent with cement hydration. Compressive strength， tensile strength， and 7 d stress-strain tests were carried out to evaluate the mechanical properties of the cement paste.Phase composition， hydration degree， and microstructure were characterized by X-ray diffraction（XRD）， thermogravimetry（TG）， and scanning electron microscopy （SEM） to investigate the effects of monomer in-situ polymerization on the internal composition and morphology of the cement paste.

Results and Discussion Experimental results indicated that the incorporation of AM and DMAA monomers did not adversely affect the slurry properties of the oil well cement. When the total monomer content was set at 1.5%， the AM：DMAA ratio was 3：1， and both the crosslinking agent （MBA） and initiator （APS） were added at 3% relative to total monomer mass， the resulting modified cement specimen （D₃） exhibited remarkable mechanical improvements after 7 days of curing. Specifically， the compressive and tensile strengths of the D₃ sample increased by 5.17% and 36.50%， respectively， compared to the unmodified reference cement. These enhancements demonstrated that in-situ polymerization could effectively strengthen the cement matrix. Moreover， the D₃ cement paste showed a significant reduction in uniaxial elastic modulus—by 38.95% relative to the blank sample—along with a 6.25% increase in peak stress. Under triaxial conditions， the elastic modulus was measured at 6.19 GPa， indicating a notable improvement in deformability. This combination of higher strength and lower stiffness was highly desirable for oil well cement applications， which require resistance to cyclic loading and downhole stress variations. XRD and thermogravimetric analysis–derivative thermogravimetry （TGA-DTG） analyses provided further insights into the micro-scale mechanisms. The TGA results revealed that the mass loss associated with the dehydroxylation of portlandite （CH） in the D₃ sample was 5.08%， which was lower than that of the blank cement. SEM observations revealed the formation of an interpenetrating organic-inorganic network structure within the cement matrix.

Conclusion The study demonstrates that in-situ polymerization of AM and DMAA can effectively enhance the mechanical properties of oilwell cement paste.According to the experimental optimization， the best toughness can be achieved when the total monomer content is 1.5%， AM：DMAA ratio is 3：1， and MBA and APS are both 3% of the monomer mass. In-situ polymerization of AM and DMAA does not produce new phases， but the interpenetrating organic-inorganic network structure is formed inside the cement paste， thereby improving its toughness.

Keywords： in-situ polymerization； toughening mechanism； oil well cement； organic monomer

Get Citation:WU Xiaolin， CHEN Jie， ZHANG Li， et al. Effects of in-situ polymerization of organic monomer on mechanical properties of oil well cement paste［J］. China Powder Science and Technology， 2026， 32（3）： 1-14.

Received:2025-09-28, Revised: 2025-12-08, Online: 2026-01-22.

DOI：10.13732/j.issn.1008-5548.2026.03.011

CLC No:TE256； TB4 Type Code: A

Serial No:1008-5548（2026）03-0001-14