Matériaux et constructions

The suitability of plaster building units to structural application is determined not only by the strength behaviour but to a large degree also by the deformation behaviour. In plaster units under permanent load there occur elastic, retarded elastic, and plastic deformations, which primarily depend on the quality of the raw materials, on placing and hardening conditions, on the structure of the hardened material, on the stress applied, and on the moisture content. The interrelations between the deformation behaviour and the above mentioned effects were investigated and—as far as as possible—plotted and mathematically evaluated. For characterizing the building material specific values such as moduli of elasticity and creep values and the conditions for its application are given.

Within the framework of the evaluation and the prediction of chloride-induced corrosion risks, simple and rapid AgNO3 spray tests can be proposed for various issues. This paper forms the first part of a series. In this first part, the Maultzsch procedure (spraying of 0.1-N AgNO3 solution + K2CrO4) as well as the procedure based on the use of a sole AgNO3 solution have been investigated on a broad range of concretes. These procedures have also been compared to the Collepardi procedure (spraying of 0.1-N AgNO3 + fluoresceine). The feasibility of these colorimetric techniques on saturated specimens cast in laboratory, after non-steady-state diffusion tests carried out in various conditions, is discussed. In addition, the results obtained from applying such spray tests in field conditions on cores drilled out from various RC test specimens exposed to a marine environment (tidal zone) and to a road and cold environment (freezing-thawing cycles and spraying of deicing salts) are presented. Colorimetric methods have in particular been applied here to the assessment of the average chloride penetration depth and of its evolution versus time (kinetics). Moreover, the detection threshold of these techniques has been investigated in various environments. The possible sources of discrepancy on the results have been analysed.

Part 3 of the present series gives the prediction formulae for the average compliance function in the cross-section of a specimen exposed to drying at constant temperature. The formulae describe the additional creep due to drying by means of the shrinkage function, which automatically introduces the consequences of diffusion theory, such as the dependence of creep on cross-section thickness and shape. The prediction formulae are compared with 19 different data sets from the literature, which reveal relatively good agreement, better than that with previous models. The main source of error is insufficient knowledge of the effect of mix composition and concrete strength. It is advisable to avoid this error by carrying out short-time measurements whenever possible.

Interim results of a long-term investigation on the durability of steel reinforcement embedded in expanded slate structural lightweight concrete are reported. The influence of concrete cover, cement content and of partial replacement of lightweight fines with natural sand was studied. Surface crazing was found to increase with cement content and increasing fine particles. The carbonation depth, and the relative permeability measured by alcohol absorption, were found to decrease with increasing cement content. Inclusion of natural sand in the mix reduced the permeability and the penetration of the carbonation front into the concrete. No instance of damage due to corsosion was found in embedded steel reinforcement after two year's exposure to industrial atmosphere.

This paper presents a comprehensive experimental and numerical investigation on hysteretic behavior of thin-walled circular steel tubes as loaded members in reticulated shells. The experimental setup available for constant compression and biaxial bending loading was designed to examine the failure process, failure modes, load bearing capacity, ductility, stiffness degradation and energy dissipation capacity of sixteen thin-walled circular steel tubes. Also, the effects of the loading condition, axial load ratio, slenderness and steel strength on hysteretic behavior of specimens were investigated. The study showed that test results of specimen loaded in two directions might overestimate hysteretic characteristic of this member. Premature local buckling may be caused by the high axial load ratio and the recommended axial load ratio may be n ≤ 0.2 to ensure the load bearing capacity, deformation capacity and ductility of circular steel tubes and to prevent the premature local buckling occurring in engineering practice. Slenderness affects the load bearing capacity, ductility, and energy dissipation capacity of specimens, and with an increasing slenderness, the stiffness degraded considerably and quickly. Specimens with high strength steel exhibited higher load bearing capacity and better stiffness but lower energy dissipation capacity than those made by low strength steel. Furthermore, the nonlinear finite element analysis was performed to simulate hysteretic behavior of test specimens, and the results got a satisfactory agreement with those of test.

When fresh mortars are applied on a substrate they lose water by suction and by evaporation, sometimes very quickly, and they start suffering some shrinkage, while simultaneously hardening and getting stiffer. Because they are adherent to a rigid background—the wall—the deformation is restrained, stresses develop in the render and are partially transferred to the background. These phenomena can generate cracks on the rendering and damage on weak or friable masonry. Air lime renders also suffer these actions, even if they react in a different way compared to cement mortars: they sometimes have high shrinkage, although they have also some ductility (comparatively high rupture energy), developing lower stresses. New␣renders to apply on old walls must be mechanically compatible with old pre-existent materials, namely with old masonry: they should not produce damage and they must be able to␣protect the wall for a reasonable period of time. In this paper a test is described to evaluate the performance of renders concerning restrained shrinkage, results obtained are discussed and conclusions are summarised about compatibility parameters and classification.

Bài báo này báo cáo về ảnh hưởng của sợi nano xenluloza (CNFs) đến các thuộc tính trong trạng thái tươi của xỉ lò cao đã hoạt hóa kiềm (GGBS). Các sợi CNFs đã được chức năng hóa bề mặt (oxy hóa) được thêm vào các hệ nhũ tương nước GGBS đã hoạt hóa kiềm (bột thủy lực). Hành vi lưu biến của các hỗn hợp bột được so sánh với xi măng Portland thông thường (OPC) và được giải thích dựa trên sự tương tác giữa bề mặt CNF và khoáng chất, và tương tác giữa CNF và nước cũng như khả năng nở. Sự phân tán nước của các CNFs với các mức độ chức năng hóa bề mặt khác nhau dẫn đến việc hình thành các gel với độ nhớt và ứng suất giới hạn khác nhau, do tính ưa nước và đặc tính hấp thụ nước khác nhau của chúng. Khi tăng mức độ oxy hóa bề mặt của CNFs, độ nhớt của sự phân tán nước của CNF giảm và sự hấp thụ nước của CNF tăng, trong khi đó độ nhớt của bột tươi tăng lên do giảm lượng nước trộn sẵn có. Trong trạng thái cứng, các bột thủy lực cho thấy sự khác biệt về cường độ cơ học liên quan đến loại và lượng CNF ảnh hưởng đến tính thấm của ma trận, như được chứng minh bởi nghiên cứu cấu trúc vi mô được thực hiện bằng vi quang phổ X-ray. Sự hiện diện của lượng CNFs cao hơn gây ra sự hình thành các khối khí rỗng có thể hoạt động như những bộ tập trung ứng suất do khả năng nở của các sợi nano.