Innovation in construction is presented as a necessary aspect in the answer that the construction industry must provide to solve its negative impact on the environment. Original and innovative ...research is only part of the work to be accomplished. More important is the implementation of innovation in practice, where traditions are strongly rooted in society, and safety and long term reliability are required. Lessons from nature and study of durable examples handed down from the pasts serve as guidelines to innovative approaches that contribute to sustainability.
New equipment and procedures for chemical and microbiological tests, simulating biogenic sulfuric acid corrosion in sewerage systems, are presented. Subsequent steps of immersion and drying, combined ...with mechanical abrasion, were applied to simulate events occurring in sewer systems. Both chemical and microbiological tests showed that the aggregate type had the largest effect on degradation. Concrete with limestone aggregates showed a smaller degradation depth than did the concrete with inert aggregates. The limestone aggregates locally created a buffering environment, protecting the cement paste. This was confirmed by microscopic analysis of the eroded surfaces. The production method of concrete pipes influenced durability through its effect on W/C ratio and water absorption values. In the microbiological tests, HSR Portland cement concrete performed slightly better than did the slag cement concrete. A possible explanation can be a more rapid colonisation by microorganisms of the surface of slag cement samples. A new method for degradation prediction was suggested based on the parameters alkalinity and water absorption (as a measure for concrete porosity).
For powder type self-compacting concrete (SCC) mixes, commonly used in Belgium, a shear thickening (Herschel–Bulkley) flow behaviour of the fresh mixes is quite often observed.
A longstanding problem ...in rheometry is the so-called “Couette inverse problem”, where one tries to derive the flow curve
τ
(
γ
˙
)
from the torque measurements
T(
N) in a (wide-gap) concentric cylinder (Couette) rheometer, with
T the torque registered at the inner, stationary cylinder and
N the rotational velocity of the outer, rotating, cylinder.
In this paper, the Couette inverse problem is approached by means of the integration method in order to convert
T(
N) into
τ
(
γ
˙
)
for a wide-gap (
R
o/
R
i
=
1.45) concentric cylinder rheometer. The approach consists in the decoupling of the flow resistance and the power-law flow behaviour after exceeding the flow resistance. The integration approach is validated by experimental verification with different powder type SCC mixtures. By means of illustration, the results of one limestone powder type SCC mixture with different superplasticizer contents are shown in this paper.
Polymer film formation in cement mortars modified with small amounts of water-soluble polymers (1% of the cement mass) is studied. A major contribution of the polymer films to the mechanical strength ...is found. Polymer bridges are detected between the layered Ca(OH)
2 crystals, on top of the cement hydrates at the air void surfaces and intermingled with the cement hydrates. Because water-soluble polymer films are highly sensitive to moisture and water, the effect of under water storage on the bridge formation is important towards the practical applications. A serious decrease of the flexural and splitting tensile strength is observed during intensive storage at high relative humidity or under water. The polymer bridges are leached under water and deposed in free spaces of the cement matrix upon subsequent drying.
Hardening of cement mortars modified with small amounts of water-soluble polymers implies both cement hydration and polymer film formation. In this paper, the effect of the presence of water-soluble ...polymers on the cement hydration reactions is investigated by means of isothermal calorimetry, thermal analysis, FT-IR spectroscopy and SEM investigation. In spite of an initial retardation of the hydration reactions, a higher degree of hydration is found after 90 days for 1% PVAA, MC and HEC modified mortars, due to a better dispersion of the cement particles in the mixing water. MC also affects the morphology of the Ca(OH)
2 crystals. Polymer bridges are detected between the layered crystals, gluing the layers together and strengthening the microstructure. Additionally, the internal cohesion of all bulk polymer modified cement pastes is improved. In the presence of the polymers, a more cohesive microstructure with a smaller amount of microcracks is created.
Biogenic sulfuric acid corrosion is often a problem in sewer environment: it can lead to a fast degradation of the concrete structures. Since the involvement of bacteria in the corrosion process was ...discovered, considerable microbiological research has been devoted to the understanding of the corrosive process. Mechanical engineers have focused on experiments comparing the resistance of several concrete mixes against biogenic sulfuric acid corrosion. Because of a lack of standardised methods, different test methods have been used, and various parameters have been modified to evaluate the resistance of the materials. The research done on sulfuric acid corrosion of concrete can roughly be divided in three groups: chemical tests, microbial simulation tests, and exposure tests in situ. In this article, an overview of the recent developments in the test methods for biogenic sulfuric acid corrosion and the obtained results are presented. Possible differences between biogenic sulfuric acid corrosion and chemical sulfuric acid corrosion are delineated.
Science and engineering intermingle in the area of construction. Engineering works, often of great dimensions and design life cycle of many decades, have to be designed on a scientific basis since ...the safety of hundreds of users depends on their design. The task of scientific institutions is to define the construction performance within categories that correspond to the contemporary level of knowledge and technology. A construction appraiser who speaks out in a way that ensures unquestionable competence about the performance of elements and buildings (existing and under construction), should be convinced of the scientific basis of his opinions. A comparison of construction sections vs. basic requirements presents an archetype of the science of construction. A matrix of the science of construction reveals its multi-faceted nature; if related to time – the issue of durability has to be considered, and if related to the scale – the complexity. Defining the construction performance in terms of technical features is a constant search for a relationship between the material model and the usability model of a building. The construction industry uses a lot of “rules of thumb”, more than any other sector of technology. In the era of computer-aided design, CAD, and building information modelling (BIM), those rules of thumb remain invaluable verification tools.
The use of polymer-modified mortar and concrete (PMM and PMC) is investigated to improve the durability of concrete sewer pipes. The aim of the research is to ameliorate the resistance of concrete to ...biogenic sulphuric acid attack through polymer modification. Prior to the durability tests, experimental research is carried out to reveal the influence of polymer modification on the physical and mechanical properties of mortar and concrete. The results of this research are presented in this paper. Due to the interaction of the cement hydrates and the polymer particles or film, an interpenetrating network originates in which the aggregates are embedded. The density, porosity and location of the polymer film depend on the type of polymer emulsion and on its minimum film-forming temperature (MFT). If air entrainment is restricted, an increased flexural strength is measured. Scanning electron microscope (SEM) analyses reveal the presence of polymer film and cement hydrates in the mortar. The polymer film causes a retardation of the cement hydration as well as a restriction of crystal growth.
PDF
