Qian Tian

The doubly thermo-responsive triblock copolymer nanoparticles prepared through seeded RAFT polymerization

The doubly thermo-responsive triblock copolymer nanoparticles of polystyrene-block-poly(N-isopropylacrylamide)-block-poly[N,N-(dimethylamino) ethyl methacrylate] (PS-b-PNIPAM-b-PDMAEMA) are successfully prepared through the seeded RAFT polymerization in situ by using the PS-b-PNIPAM-TTC diblock copolymer nanoparticles as the seed. The seeded RAFT polymerization undergoes a pseudo-first-order kinetics procedure, and the molecular weight increases with the monomer conversion linearly. The hydrodynamic diameter (Dh) of the triblock copolymer nanoparticles increases with the extension of the PDMAEMA block. In addition, the double thermo-response behavior of the PS-b-PNIPAM-b-PDMAEMA nanoparticles is detected by turbidity analysis, temperature-dependent 1H-NMR analysis, and DLS analysis. The seeded RAFT polymerization is believed as a valid method to prepare triblock copolymer nanoparticles containing two thermo-responsive blocks.

In situ synthesis of thermo-responsive ACB triblock terpolymer nanoparticles through seeded RAFT polymerization

Seeded RAFT polymerization is proposed to prepare thermo-responsive ACB triblock terpolymer nanoparticles of poly[N,N-(dimethylamino) ethyl methacrylate]-block-polystyrene-block-poly(N-isopropylacrylamide) (PDMAEMA-b-PS-b-PNIPAM) containing a middle hydrophobic C block and two thermo-responsive blocks A and B. Following this seeded RAFT polymerization, the nanoparticles of the AC diblock copolymer containing a thermo-responsive block of poly[N,N-(dimethylamino) ethyl methacrylate] (PDMAEMA) are prepared through the macro-RAFT agent mediated dispersion polymerization, and then the in situ synthesized AC diblock copolymer nanoparticles are used as seed in the RAFT polymerization, onto which the other thermo-responsive B block of poly(N-isopropylacrylamide) (PNIPAM) is introduced. The synthesized triblock terpolymer nanoparticles contain a hydrophobic core of the middle polystyrene (PS) block and a mixed corona of two thermo-responsive PNIPAM and PDMAEMA blocks. The thermo-response of the PDMAEMA-b-PS-b-PNIPAM nanoparticles is checked, and the morphology of the triblock terpolymer nanoparticles during the thermo-responsive phase transition is detected. The proposed seeded RAFT polymerization is believed to be a valid method to prepare ACB triblock terpolymer nanoparticles containing two thermo-responsive blocks.

Determining the Contact Angle of Hardened Cement Paste Using Thin Layer Wicking Method

Contact angle is a very important parameter to investigate the function mechanism of chemical admixtures as well as the capillary stress resulted from self-desiccation or drying. However, in most of the studies, it is only assumed to be 0 degrees. This paper studied the contact angle of hardened cement paste using thin wicking method. A serious of study was conducted on the influence of layer preparation, pre-contacting method, cement paste powder size, and suspension concentration on the measuring results. An optimized thin layer wicking method was proposed for determining the contact angle of hardened cement paste, which improves effectively the linear correlation of the penetration distance - time curve and satisfies the prerequisite of Washburn function.

Autogenous Volume Deformation of Concrete due to MgO under the Temperature History of a Diversion Tunnel Concrete

Using MgO type expansive agent is considered as a convenient and effective method to reduce cracks in dam concrete, but the research on autogenous volume deformation of concrete with MgO type expansive agent under the temperature history of real structure is still unclear. In this paper, the temperature history of a diversion tunnel concrete was selected to discuss the autogenous volume deformation of concrete with different activities and dosages of MgO type expansive. The results showed that the autogenous volume expansion of concrete with MgO type expansive agent increased with the content and the activity of MgO type expansive agent. The expansion values of concrete with the content of 4%, 5% and 6% MgO type expansive agent are 51×10-6, 85×10-6 and 105×10-6 in temperature rise stage, and 43×10-6, 56×10-6 and 71×10-6 in temperature decrease stage. The expansion values of concrete with the activity 31s, 138s and 240s MgO type expansive agent are 36×10-6, 51×10-6 and 66×10-6 in temperature rise stage, and 32×10-6, 43×10-6 and 62×10-6 in temperature decrease stage. After 150d the autogenous volume deformation due to MgO type expansive agent did not increase any more.

Device for Pore Solution Extraction from Cement-Based Materials and its Application

In this paper, a device for pore solution extraction from cement-based materials was presented, The relevant Factors of Efficiency of Pore Solution Extraction and the effects of squeezing pressures on the chemical concentrations of pore solutions were studied. The results shows, the efficiency of pore solution extraction can be effected by pressure values, squeezing duration, pressure maintaining time; A low rate of pressures loading is suitable for early-age cement pastes, and long-term samples can take larger rate; 30 minutes loading time can be adopted for specimens with all the different ages; no significant differences were observed regarding the chemical composition (Na and K) of the pore solution extracted between 300 and 900MPa.

The Relationship between the Water Absorption Capacity of SAP and the Amount of Entrained Water in HPC

Using SAP is considered as an effective method to counteract autogenous shrinkage of HPC, but the research on the relationship between the water absorption capacity of SAP and the amount of entrained water in HPC is still unclear. In this paper, 6 SAPs with different water absorption capacity were made to discuss the workability and mechanical property of HPC with SAP when different amount of water were entrained. The results showed that the bigger distilled water absorption capacity of SAP is, the smaller the fluidity of cement paste mixed with SAP is, SAP used in HPC should own bigger synthetic pore fluid absorption capacity and smaller distilled water absorption capacity. When 0.03g water/g cement was entrained, the slump of concrete mixed with 4#, 5# and 6# SAP is the same as the slump of ref concrete, and the compressive strength of concrete mixed with 4#, 5# and 6# SAP is also the same as the compressive strength of ref concrete.

Research on the Restraint Expansive Stress of MgO Reinforced Concrete at the Early Age

To solve the problem of early-age concrete shrinkage under constraint, 0%, 2%, 3%MgO expansion agent are mixed in the concrete. Results indicate that MgO expansion agent can ensure the expansion strain of the concrete and produce the self-stress under constraint which is up to 1.8Mpa~2.2Mpa.

Determination of Tensile Creep and Stress Relaxation of Concrete by Ring Test

The understanding of stress relaxation and tensile creep behavior is extremely important in accurate stress analysis and crack prediction of early-age concrete. The free shrinkage deformations of concrete with different strength grade were examined. The early-age tensile elastic modulus of concrete was investigated through temperature-stress testing machine. The tensile creep and shrinkage stress were obtained through the modified restrained ring test. The results indicate that the development of free shrinkage coordinates well with the inner strain of steel ring. Tensile creep decreases as water-binder ratio increases. Creep counteracts tensile stress of concrete by 28%~40% , decreases the possibility of cracking of concrete at early ages.

The High Performance Concrete Curing Agent Based on Polyacrylic Emulsion with Hydroxyl Monomer HPMA

The influence of the chemical structures of styrene/butyl acrylate/hydroxyl propyl methacrylate emulsion on some properties of ordinary Portland cement concretes has been investigated as concrete curing agent. The structural parameters that are varied included the fractions of HPMA and the polymer structure of the shell-core. The result of the study showed that the hydroxyl monomer HPMA played an important role on the improvement of water retention and the optimal proportion is about 5 wt% of the polymer. In addition, the shell-core structure of the emulsion with HPMA located in shell polymer can further enhance the water-retention rate. Besides, the emulsion with hydroxyl groups could smooth the surface of the concrete, inhibit the carbonation and had positive influence on the compressive strength.

Effect of Different Forms of CaO on the Properties of Cement-Based Materials Containing High Content of GGBFS

The effects of different forms of CaO on performances of cementitious binders containing 50 wt. % GGBFS powder are studied using compressive strength testing, hydration heat and X-ray diffraction measuring, microstructure measuring, and deformation testing. Results show that, the use of analytical-grade CaO or calcined CaO expansive clinker produces a higher mechanical strength than analytical-grade Ca (OH)2 for mortar samples. The mortar containing analytical-grade CaO or calcined CaO expansive clinker shows a strength increase higher than the reference before 14 days of curing, but a litter lower than the reference after 28 days. With the increase of curing age, the diffraction peaks of Ca (OH)2 gradually weaken, while those of C-S-H and hydrotalcite gradually increase, contributing to a gradual increase in strength of GGBFS pastes. Compared to analytical-grade CaO, the expansive process of calcined CaO expansive clinker matches better to the deformation history of mortar containing large content of GGBFS. This work is of great significance to explore the potential use of different forms of CaO as an alternative activator for GGBFS.