Hydration Mechanism And Physical Properties Of SrAl2O4
In our impression, conventional concrete is an opaque material and concrete structures are dull and gray which does not allow light to pierce its interior and reflects few. As a result, concrete buildings and roads are lighted up by lamps at night for decoration and safety. Thus, more electricity is consumed and more greenhouse gases are produced with much pressure on our atmosphere and environment. To cope with the problems, scientists and engineers come up with new ideas for the modification of concrete and developed light-emitting concrete. Recent years, with the acceleration of development of smart buildings and highways the outstanding performance of light emitting concrete, attracts much attention and various types of concrete have been developed. Over the past decade, various light-emitting concrete has been developed and applied to actual practice. Light-emitting concrete is considered as an Eco-friendly concrete because of less carbon dioxide is discharged to into the atmosphere and less light pollution is produced in our living environment. Light emitting concrete is a type of smart and multifunctional concrete that possess the ability to store solar energy or artificial light and emitting it as visible light in the dark. It is also called self-luminous concrete. It is powered by the sun or other lamps without electricity consumed. The Light emitting concrete is made by adding phosphor aggregate to the conventional concrete. In order to make conventional concrete absorb and to emit light in dark, the easy way is to take advantage of phosphor aggregate and powder. At present, there are three main feasible approaches to manufacture light-emitting concrete,
- by mixing phosphor aggregate and powders into conventional concrete
- modifying the microstructure of the concrete
- covering the concrete surface with a luminous coat.
To enable traditional concrete to store and emit light by itself, researchers adopt the phosphor materials and mix them into concrete as a component. Usually, normal aggregates are totally or partially replaced by phosphor ones and a moderate amount of fluorescent powders are added into the concrete mixtures. A company named Ambient Glow Technology (AGT) developed a new concrete with the light-emitting aggregates that absorb and store energy from both the sun and artificial lights. Once the light source is no longer present, they begin releasing their stored energy by glowing. They utilize a proprietary formulation of powerful, photoluminescent pigments, so they will emit their glow for 12 hours or longer to provide a self-generating light emitting source. The aggregates and powder can be fully charged in 10 minutes when exposed to natural light. Direct sunlight is not required and the phosphor can be fully energized in 15-20 minutes using halogen or fluorescent light sources. The aggregates and powder will continue to glow for over 20 years with a glow degradation of about 1 – 2% per year. After 20 years, they will be performing at 60% capacity.
Three optional colors are available: Aqua Blue, Sky Blue, and Yellow-Green. The Technology Center of China West Construction Group developed a marble-imitated light-emitting concrete by adding inorganic pigment and adding non-radioactive long afterglow phosphor aggregates and polishing its surface, which had the capability of storing light energy and emitting light in the darkness. With different optional colors, this type of concrete not only possess the quality glowing in dark but also possess high decorative quality. This concrete enjoys a broad application prospect in building decoration/road lighting and has been used in practical engineering projects in Sichuan province of Western China.
Nazarov et al., set out to make an experimental artificial glow reef from concrete and sand to provide a hard surface. The main goal of these reefs was to allow the future cultivation of algae to attract the fish. For this purpose, the artificial block must be luminescent and preferably emit green light. They proposed to use the persistent phosphor SrAl2O4: Eu2+, Dy3+ as a phosphorescent material. In this study, an epoxy layer of SrAl2O4: Eu2+, Dy3+ phosphor was deposited on the reef surface by a brushing technique. Multiphase blue-green persistent phosphor with turquoise luminescence was synthesized and applied for sea investigation. For the first time the experiments with artificial stone covered by SrAl2O4: Eu2+, Dy3+ based phosphor were carried out in real sea conditions in Pulau Payar Marine Park Malaysia. Strong and bright blue-green luminescence was observed and registered under the water.
Wang from Shenyang Jinzhou University developed a new type of light-emitting concrete by mixing phosphor powders that can emit light after excited by the sun ray. She tested the luminous performance and gave out an optimum mixing dosage of phosphor powders. By using the adoption of the high-temperature solid-state method, the phosphor powder emitted the large intensity of light. The peak frequency of this phosphor material was 480 nm while the absorption spectrum was mainly at the ultraviolet region, which was able to turn invisible sunray to visible light. The research shows that the light-emitting duration of the excited concrete gets longer when the phosphor powder content is increased, while the mechanical properties suffer a degradation.
Researchers at Purdue University developed a Soy-based luminous sealant, a mixture of soy methyl ester polystyrene and strontium aluminate that slowly luminesced after being excited by light. The sealant covered the surface of the common concrete and a type of new light-emitting concrete was completed. The magnitude and duration of the concrete surface were quantified to evaluate its performance. The result indicates that the luminesced surface emits light for approximately 24 hours in the dark place after being excited and the larger particles of strontium aluminate luminesce for a long time against the smaller particles. Light-emitting concrete has excellent performance of long duration of light emitting and long span without consuming any electricity, which is considered as a promising smart and sustainable low carbon concrete. Due to the gentle light emitted by the concrete and less light pollution generated, both human beings and wild creatures are less disturbed at night and we are able to create more liable and eco-friendly environment. Unlike electricity powered lamps, Light-emitting concrete can emit light in dark without complex support devices and does not require frequent maintenance. The safety of highway is always a significant issue for drivers and the government. Conventional highway signs lines only reflect the light of vehicles at night, and its brightness and clearness are not enough to guarantee the safety of driving. The introduction of light-emitting concrete not only offers bright and clear sign lines but also make drivers relax and feel better. The first pilot of glowing lines has been realized at the N329 in Oss, the Netherlands. In China, the self-emitting concrete is introduced to tunnels whose concrete surfaces are covered by fluorescent coats and has been used in expressway tunnels.
The study of light-emitting concrete is rather rare and unsystematic, so more detailed research work will be required. Mixing of Fluorescent powders and aggregates will affect the strength of concrete. Research work is required to investigate the hydration of cement paste, physical and mechanical properties of concrete and mortar.
