Study on the performance of a new type of water-repellent admixture for cement mortar

A special water repellent for mortar is made from the combination of polyacrylamide as a principal raw material and FDN-2 as an additive. Every item of comparison test and research for the technical features of the compound water-repelling admixture (CWRA) has been carried out in building antiseepage mortar. The result shows that the main properties of the mortar have satisfied China's national standard. The permeability of mortar added with the agent has been greatly improved. The mortar has high effective penetration resistance and good workability. This paper discusses the waterproofing mechanism of the agent.     

Rheological properties of cement pastes: A discussion of structure formation and mechanical property development

The objective of this paper is to examine the evolution of rheological properties (e.g. yield stress) and to evaluate the use of these properties as a method to monitor structure formation and mechanical property development (i.e. setting) in cementitious materials. The authors utilize the stress growth technique to assess the development of a solid structure in cement pastes. An increase in the yield strength of the system due to cement hydration is identified to occur near the end of the dormant period as identified by chemical shrinkage. The transition from a fluid to a solid state and the development of elastic properties in the material are both noted to occur prior to the time of initial set as identified by the Vicat needle.     

Evidence of anomalous thermal expansion of water in cement paste

A comparative study of permeability measurement by thermopermeametry (TPA) and beam bending was performed on cement paste. To bring the two measurements into agreement, it is necessary to recognize that the pore solution has a thermal expansion coefficient about one and a half times that of bulk liquid and to account for viscoelastic stress relaxation during TPA experiments. The anomalous thermal expansion is not accounted for by the presence of ions in the cement paste pore solution.     

Genetic algorithm in mix proportioning of high-performance concrete

High-performance concrete is defined as concrete that meets special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practices. Ever since the term high-performance concrete was introduced into the industry, it had widely used in large-scale concrete construction that demands high strength, high flowability, and high durability. To obtain such performances that cannot be obtained from conventional concrete and by the current method, a large number of trial mixes are required to select the desired combination of materials that meets special performance. Therefore, in this paper, using genetic algorithm that is a global optimization technique modeled on biological evolutionary process—natural selection and natural genetics—and can be used to find a near optimal solution to a problem that may have many solutions, the new design method for high-performance concrete mixtures is suggested to reduce the number of trial mixtures with desired properties in the field test. Experimental and analytic investigations were carried out to develop the design method for high-performance concrete mixtures and to verify the proposed mix design.     

Permeability and diffusivity of concrete as function of temperature

Tests have been carried out on 11 types of concrete—ranging from normal-strength to high-strength concrete, to polymer-modified and self-compacting concrete—establishing permeability and diffusivity of concrete as a function of temperature between 20 and 80 °C. The results show a considerable increase of these properties with temperature. Theoretical prediction on the basis of thermodynamics shows reasonable to good agreement between theory and experiment.     

Influence of the kneading water content in the behaviour of single-coat mortars

The effect of water content in the kneading process of mortars for application as single-coat renders was evaluated in terms of several properties. These properties refer to the mortar product in the fresh and hardened state. Characteristics under evaluation in function of kneading water are, for fresh mortar, the apparent density and entrained air while, for hardened products, apparent density, shrinkage, mechanical properties, abrasion wear and permeability amongst others. If some of these characteristics are obtained by standard tests, others, like abrasion wear, had to be adapted and are described here.Both for fresh and hardened products characteristics, kneading water amount significantly changes them and it was possible to establish the proper content of water to be used in order to get a well-behaved single-coat mortar.     

Modification of the wettability of polymer surfaces using nanoparticles

The effects of nanoparticles, embedded into the matrices of polymer films, on the wettabilities of the surfaces of the composite films are investigated following a two-fold procedure. First, five particles such as silica (of two sizes), tin oxide, alumina and zinc oxide ranged from 7 to 100 nm are mixed with a poly(methyl siloxane). Second, silica nanoparticles (7 nm) are embedded in five different polymers such as poly(methyl methacrylate), polystyrene and three poly (alkyl siloxane) products. Nanocomposite films are produced by adding nanoparticles in the polymer solutions which are then sprayed on silicon substrates.     

Influence of superplasticizers on rheological behaviour of fresh cement mortars

To assure required workability of high performance concrete (HPC), various superplasticizers are used. Only by using superplasticizers can rheological properties of HPC mix be adequately adjusted to the methods and conditions of concrete processing. Thus, the key element in efficient workability shaping is the complex knowledge how superplasticizers influence the rheological properties of fresh concrete in different technological circumstances.In the paper, the methodology and test results of an investigation into the influence of chemically different superplasticizers on the rheological properties of standard mortars are presented and discussed. The rheological parameters of mortars yield value g, and plastic viscosity h were determined using VISCOMAT PC rotational rheometer. In the research, the influence of the performance of superplasticizers was investigated taking into account following factors: chemical origin of superplasticizers (SNF/naphthalene sulfonic acid/, AP/polycarboxylate acid, PC/policarboxylate ester/), superplasticizer dosage, W/C ratio, cement type (CEM I, CEM II and CEM III), cement physical and chemical properties and temperature.The results presented in the paper show that by testing rheological parameters of mortars with rotational viscometer, it is possible to complex and precisely determine the performance of superplasticizers. On the ground of obtained results, it is possible to optimise the composition of mortars and concretes from workability point of view.     

Strength, permeability, and carbonation of high-performance concrete

This investigation is aimed at developing high-performance concrete and form part of an investigation into the optimization of a blended cementitious system for the development of high-performance concrete. Binary and ternary blended cementitious systems based on ordinary Portland cement (OPC), pulverised fuel ash (PFA) and silica fume (SF) were investigated. PFA up to 40% was used, and to these blends, 0%, 5%, 10% and 15% SF were incorporated as partial cement replacements. Results of compressive strength, tensile strength, oxygen permeability and carbonation of concrete are reported. A water-binder (w/b) ratio of 0.27 was used for the main group of mixes and w/b ratios of 0.40 and 0.50 were used for some selected mixes. Based on the experimentally obtained results, prediction models were developed which enabled the establishment of isoresponse contours showing the interaction between the various parameters investigated. It was found that the incorporation of 8-12% SF as cement replacement yielded the optimum strength and permeability values.     

Crack effects on gas and water permeability of concretes

The relationship between load-induced cracking and concrete permeability is studied. Ordinary concrete (OC) and high-performance concrete (HPC), including steel fiber-reinforced concrete (HPFRC), are used. Two discs, 50 mm-thick slices, cut from 110-220 mm cylindrical specimens are diametrically loaded, as for a normal splitting test. The lateral displacement, also called the crack opening displacement (COD) is monitored for each loading cycle. After unloading, gas and finally water permeability tests are both performed, using constant head permeameter, to compare the influence of the percolating fluid and the COD. Due to the wide range of measured gas flow, Klinkenberg's and Dupuit-Forcheimer's laws are applied to compute the intrinsic gas permeability. Results suggest it increases proportionally to the cube of the COD and it matches water permeability, if only the first water percolating time is considered. The roughness parameter of the cracks induced in each concrete, is compared and discussed.     

Permeability and self-healing of cracked concrete as a function of temperature and crack width

Tests have been carried out on a high-strength concrete establishing permeability and self-healing behaviour of cracked concrete as a function of temperature between 20 and 80 °C and crack width between 0.05 and 0.20 mm. The results show a considerable increase of water transport with temperature. Theoretical prediction on the basis of thermodynamics showed reasonable to good agreement between theory and experiment.     

聚羧酸减水剂在水泥颗粒表面的吸附行为

合成一系列聚羧酸减水剂,探讨不同单体摩尔比对其吸附性能的影响。结果表明,当n(烯丙醇聚氧乙烯醚)∶n(2-丙烯酰胺-2-甲基丙磺酸钠)∶n(丙烯酸)∶n(马来酸酐)=1∶0.14∶3.6∶2.6时,产物吸附性能最优。并利用总有机碳分析技术,研究了不同温度、不同浓度下最优产物在水泥颗粒表面的吸附动力学和热力学。动力学研究结果表明：聚羧酸在水泥颗粒表面的吸附过程符合Lagergren吸附速率方程,吸附速率常数k=0.01594 min-1(30℃),表观活化能Ea=17.9647 kJ·mol-1。热力学研究结果表明：随温度升高,聚羧酸在水泥颗粒表面的吸附量增大;求得吸附热力学参数分别为ΔHad=-24.788 kJ·mol-1,ΔSad=0.050 kJ·mol-1·K-1,ΔGad=-39.886 kJ·mol-1(30℃),可知该吸附过程是自发的放热反应。理论上温度升高对吸附不利,但因放出的热量促进水泥水化,导致聚羧酸分子容易掺杂到水化产物中,从而使更多聚羧酸吸附到水泥颗粒表面,令其吸附量反而增大。     

Evaluation of the performance of sulfonated esparto grass lignin as a plasticizer-water reducer for cement

The objective of the work described in this first paper of a series is an investigation of the preparation of a sulfonated esparto grass lignin (SEL) and its behavior as a plasticizing-water-reducing agent for cement-water systems. SEL is prepared by extracting the lignin from the black liquor of a soda esparto grass pulping process and then sulfonating it with a mixture of sodium sulfite and formaldehyde.Analyses and characterization of SEL carried out with high-performance size exclusion chromatography (HPSEC), reversed phase chromatography (RPC), infrared spectrometry and chemical methods show that both the molecular weight average and the combined sulfur content are relatively high. Moreover, HPSEC shows that SEL has a relatively more uniform molecular weight distribution (MWD) than the commercial products obtained from the sulfite wood pulping process. On the other hand, SEL could reduce the water content, improve the workability and compressive strength of mortars. SEL also permits a very low rate of slump loss of cements without excessive extension of the final set time.     

Proliferation rate of fibroblast cells on polyethylene surfaces with wettability gradient

Surface wettability on anchorage‐dependent cells has an important role in cell growth rate. In our previous studies, we prepared a wettability gradient on polyethylene (PE) surfaces using corona discharge treatment from a knife‐type electrode whose power increased gradually along the sample length. The PE surfaces were oxidized gradually with increasing power and characterized by Fourier transform infrared spectroscopy, contact angle goniometry, and electron spectroscopy for chemical analysis. The purpose of this study is to determine the rate of proliferation on polymer surfaces with different wettability. The behavior of cell growth for NIH/3T3 fibroblast cells attached on the polymer surfaces with different hydrophilicity was investigated using wettability gradient PE surfaces prepared by corona discharge treatment. They were investigated for the number of grown cells from 24 to 60 h in terms of surface wettability. From the slope of cell number on PE gradient surface versus culture time, the proliferation rates (number of cell/cm² · h) were calculated. It was observed that the proliferation rate was increased more on positions with moderate hydrophilicity of the wettability gradient surface than on the more hydrophobic or hydrophilic positions, i.e., 1111 (number of cell/cm² · h) of 57° of water contact angle at the 2.5‐cm position (P < 0.05). This result seems closely related to the serum protein adsorption on the surface: the serum proteins were also adsorbed more on the moderately hydrophilic surface. In conclusion, surface wettability plays an important role in cell adhesion, spreading, and proliferation on the polymer surfaces. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 599–606, 2004     

A model for the flow of cement pastes

This paper presents a simple mathematical model of the flow behaviour of fresh cement pastes and mortars based on a soil mechanics approach. A soil mechanics model can mimic many of the features of the pastes rheological behaviour indicating that physical, as well as chemical, factors might control many of these.Specifically, we have developed a simple mathematical model of the evolution of the packing of the clinker or sand grains and its effect on the flow of the paste or mortar. This not only incorporates the role of the pore water but also copes with the large deformations typical of the mixing and placement of mortars. This model is used here to simulate small cyclic deformations with a large drift accumulating in one direction, and is able to capture both the liquefaction and locking phenomena seen in practice when mortars are vibrated.     

A study on the process for formation of spherical cement through an examination of the changes of powder properties and electrical charges of the cement and its constituent materials during surface modification

In the initial stage of surface modification treatment to form cement particles into a spherical shape, the fine cement particles below 3 μm increased and the specific surface area also increased. However, in the final stage of treatment, both the fine particles and the specific surface area decreased when compared to raw cement. These results seem to endorse a process for formation of spherical cement, namely grinding of the particles in the initial stage and then adhering and fixing the fine particles to the surfaces of larger core particles in the next stage. Clinker powder had a positive charge, whereas gypsum powder had a negative charge. The difference observed in the electrical charge proved that the attachment of gypsum particles to clinker particles was caused by the attraction of opposite charges in addition to the van der Waals interaction. Therefore, gypsum played an important role as an adhesive agent. The fluidity of clinker powder after it was treated with finely ground gypsum improved. This was because the fine gypsum particles quickly attached to the surfaces of the larger particles of clinker, and consequently, the final process for formation was accelerated.     

Evaluation of mixing and application process parameters of single-coat mortars

The effects of different preparation and application conditions of single-coat mortars in their characteristics as fresh and hardened products are described in this work. The parameters under consideration were mixing water, mixing and resting time of the fresh mortar. Tests were made in the fresh mortar like apparent density, amount of entrained air and water retention. Tests with the hardened mortar also included mechanical strength and capillarity evaluations. Finally, practical cases were considered and here some application parameters were studied. It was possible to conclude on some important parameters affecting both the processing and application of single-coat mortars.     

Influence of fly ash and its mean particle size on certain engineering properties of cement composite mortars

An experimental investigation on the effects of incorporating large volumes of fly ash on the early engineering properties and long-term strength of masonry mortars is reported. The effect of fly ash and its mean particle size (PD) on the variation of workability and strength has been studied. It was found that fly ash and its mean particle size play a very significant role on the strength of masonry mortars. It has been observed that the early-term strength, except the mortars incorporating coarse fly ash (CFA), was slightly influenced by the replacement with fly ash. The long-term strength (both the bond strength and the compressive strength) will significantly increase, especially for the bond strength of mortars incorporating coarse fly ash. It was also found that the bond strength significantly increased as the mean particle size of fly ash decreases after 28 days curing. However, the 7-day strength was little influenced by fly ash particle size. The fluidity of composite mortar enhanced due to replace cement and lime with fly ash, and the mean PD of fly ash significantly influenced the workability.     

Influence of inorganic pigments on the fluidity of cement mortars

Among the admixtures used for cement composites, an inorganic pigment, which contributes color to the final product, enhances the esthetic value of a building. It can be reasonably assumed that the use of inorganic pigments will increase, given the recent trend to make cities more beautiful with color. The aim of this study was to investigate the effects of inorganic pigments on the fluidity of cement mortar. For this purpose, a flow test was carried out on cement mortar mixed with inorganic pigments by changing the proportion of cement mortar, water-cement ratio, and ratio of pigment. When red and yellow pigment mortars were used, the fluidity rapidly decreased with increasing ratio of pigment. To secure an acceptable workability, the amount of mixing water had to be increased or a superplasticizer employed. When a green pigment mortar was used, however, the fluidity of the mortar recorded −2.4-6.9%, indicating almost no change in flow. When a black pigment mortar was used, the pigment had no effect on fluidity.