Advanced Materials Research Vols. 168-170

Abstract: The paper mainly researched the influence of salt admixtures on foam stability of air-entraining admixtures (AEAs). Foaming power and foam stability of SJ-2 and DH-9 were analyzed. The results indicated that calcium chloride and calcium nitrate reduced the foaming power regardless of kinds of AEAs. On the contrary, sodium sulfate and sodium nitrite increased the foaming power, but with the increase of their added content, the foaming power taked on the tendency of descension. In addition, these four salts declined the foam stability of SJ-2 and had hardly effect on that of DH-9.

Abstract: In this paper, the whole stress-strain curve of concrete attacked by sulfate and sulfate-chloride compound were investigated experimentally by an accelerated deterioration laboratory technique. For practical engineering applications, special attention of research was devoted to an ultrasonic nondestructive test (NDT) technique to estimate the damage extent. The curves were fitted very well with the same form of equations for the concrete suggested in the structure design code, but with different coefficients and value of feature points. Aanlytical expressions between the corrosion damage of concrete attacked by sulfate and the stress-strain relationship, constitutive parameters, value of character ponits,a series of mechanics parameters are achieved, which can be directly used in theoretical and numerical analysis as well as practical engineering detection and assessment of concrete structures attacked by sulfate.

Abstract: This study offers a new isotropic non-linear elastic incremental constitutive model for concentrically loaded specimens based on non-linear elasticity theory, according to the test results of 18 concrete stub columns wrapped with different amount of carbon fiber reinforced plastics(CFRP), glass fiber reinforced plastics(GFRP), steel ring, FRP-steel ring, respectively. The mechanical proprieties of concrete stub columns with circular cross section wrapped with any material under uniaxial loading can be analyzed according to the proposed constitutive model, the failure criterion of concrete in complex stress state, and the ultimate tensile strain of wrapping materials. The calculated results are in good agreement with the measured results.

Abstract: It has been the consensus shared by every member of the society that we should protect the earth, benefit the future generations and take the road of sustainable development which is natural-based and coordinated with environment carrying capacity. Currently, no one can doubt the importance of low carbon living and low carbon architecture. Numerous new materials and high technologies have been used in the country all over the world in the course of low carbon architecture’s development, some of which has had a favorable result, such as London zero carbon emissions pavilion at the 2010 Shanghai World Expo. But China still is a developing country, for various reasons, it is premature to widely promote the expensive high-tech low-carbon buildings, and especially in the vast rural areas, the traditional local materials and suitable technology still could have general applicability. This paper takes the rammed earth building as example, by introducing the history of rammed earth building, the application status and some of the latest instances, and summarizes several advantages of rammed earth building: the first is that easy manufacturing processing could reduce the energy consumption; the second is that local materials could lower transportation costs; the third is that the clay materials with good thermal performance such as heat insulation and moisture property could ensure comfortable indoor environment, the last is that long service life and easy reclamation could recycle building materials. Then the author looks forward to the future development trends of rammed earth buildings, explores the new construction practices of rammed earth buildings. Finally this paper concludes that traditional local materials and suitable technology would play an important role in the modern low-carbon architecture.

Abstract: This paper proposes a new classification of strength theories of concrete based on mathematical representation. First, stress invariants in strength criteria are classified according to their geometrical meanings in the stress space. Then, strength criteria of concrete are classified according to the categories of stress invariants employed in their representations and subclassified according to the nonlinear terms involved. By this formal classification, the mathematical properties of strength theories of concrete can be analyzed more clearly for constitutive formulation.

Abstract: The abrasion resistance of concrete has been becoming more and more attention, this paper used ball bearing abrasion resistance test (GB/T16925-1997) to investigate the influence of mineral admixture on concrete abrasion resistance. Results indicates that concrete which is higher w/b (w/b = 0.5) can improve its abrasion resistance at 90d age when mixed with fly-ash, while mixed with both fly-ash and slag can improve its 28d and 90d abrasion resistance. Concrete which is lower w/b (w/b = 0.31), either mixed with fly-ash or with both fly-ash and slag, its abrasion resistance at 28d and 90d descends as well as the mixture content increased.

Abstract: A research program was undertaken to discover the corrosion mechanism of portland cementitious materials to acid rain attack in China. The deterioration process and corrosion products of hardened ordinary portland cement pastes in pH 2 simulated acid rain solution were analyzed by XRD and BSE. The results indicate that the destruction of hardened portland cementitious materials by acid rain attack in China is predominantly due to the coordinated effect of H+ and SO42- of acid rain solution, and gradually occurs from the surface to the interior of materials. The corrosion products are mainly a white mushy mixture consisting of silica gel (SiO2•nH2O), alumina gel (Al2O3•nH2O) and dihydrate gypsum (CaSO4•2H2O) crystal. During the process of acid rain attack, the deteriorated specimen can be divided into corrosion layer, affected layer and unaffected layer.

Abstract: Different gradation types may have different particle contact behaviors for asphalt mixture, so that it holds diverse pavement performances. The particle contact theory explains the particle contact behaviors law during movement. A particle contact behaviors model was established, which is easy to describe and apply on the spot. A line contact stiffness model was used to simulate particle contact behaviors for gradation types of CA0.2, CA0.4, CA0.6 and CA0.8 when particle of asphalt mixture is moving with dead weight. Their pavement performances were verified with Marshall test, wheel tracking test, gyratory compacting test and the index of potential energy test under optimum asphalt content. Test results show that their service performance is identical to simulation result of particle contact during movement with dead weight. With the help of the research, it can supply some theoretical and applicative bases for an optimum mixture gradation design and indoor gradation simulating design for asphalt mixture.

Abstract: According to the method of semi-immersion in 5% sodium sulfate solution, the property against sulfate attack of cement-based materials with various compositions are studied with the indexes of the amount of crystal salt in unit exposing area and the ratio of total mass change. The experiment indicates that the order of mortar with w/c=0.4 against sulfate attack from high to low are SAC 42.5>PO 42.5>Clinker>HAC 42.5. When w/b is constant and the cement was replaced by the same quantity of salic material, the order of mortar against sulfate attack are Clinker> PO 42.5> SAC 42.5> HAC 42.5. The replacement of SAC and HAC with the same quantity of salic material leads to the sharp decrease of its property against sulfate attack while the result is opposite for the clinker serial and PO 42.5 serial. Addition of redispersible polymer powder can lead to decrease of penetration and increase the properties of products to sulfate attack. Then, it comes to the conclusion that multi-binder with PO.42.5cement 70%–80% (quality percentage), and internal mixing of 5%–10% silica fume, 10%–15% fly ash can meet the high corrosion resistance requirements.

Abstract: Reasons of pathological changes of Lingnan ancient stone bridges are elaborated in this paper, classification of pathological changes and procedures of protection are discussed, methods of elimination of pathological changes and protection are also probed into. The purpose of this paper is to initiate people to have profound understanding to pathological changes of Lingnan ancient stone bridges to protect them in modernization strategy.