HDPE土工膜用于屋面隔根层防渗隔根双重作用研究
HDPE土工膜用于屋面隔根层处理--用于屋面隔根层防渗隔根双重作用研究
随着我国改革开放的深化和城市化程度的不断扩大，人们赖以生存的城市空间也变得越来越小。为了提高城市的绿化覆盖率、改善生态环境、美化城市景观，实施屋面绿化是有效的途径。
一、发展种植屋面
势在必行在现代化社会迅猛发展的今天，我国大中城市的土地资源已是“”，可以用于绿化的土地面积越来越少。然而，数以亿计的屋面多是光秃秃的，而充分利用这块尚未绿化的“空地”发展种植屋面，势在必行。
1、发展种植屋面，减缓城市的“热岛效应”
建筑物表面温度与时间关系
由于各类建筑的屋面、墙体以及道路等均属于性能良好的“大型蓄热器”，它们白天吸收太阳光的辐射能量，夜晚放出热量，造成市区夜间的气温居高不下，导致市区气温比郊区气温升高2～3℃。因气温升高部分呈岛状，故称其为“热岛效应”。如能将屋面建造成种植屋面，在屋面上广泛种植花、草、树木，通过屋顶绿化，实现“平改绿”，不但可以限度地提高城市的绿化覆盖率，而且可以有效地缓解城市的“热岛效应”。据报导，每公顷绿地每天能从环境中吸收的热量，相当于1890台功率为1000瓦空调的作用。
2、实施屋面绿化
有利于增加城市大气中的氧气含量屋面绿化可以通过植物的光合作用，吸收大气中的二氧化碳，放出氧气，便于维持空气中二氧化碳与氧气的平衡，提高空气质量，据测定，24平方米早熟禾草坪，一昼夜可制造氧气1380克，足以供给一个成年人正常生活1天所需要的氧气；一株山毛榉一昼夜则可吸收二氧化碳2352克，并放出氧气1712克，起到净化空气的作用。
3、屋面种植的植物
可吸收有害物质，减轻大气污染屋面的植物具有吸咐、固定尘埃、重金属元素和吸收大气中的NH3、SO2、NO2、HF和CL2等有害物质，并具有降低城市的噪音功能。据测定，120mm厚的植物层隔音达40分贝，故可明显降低大气和噪音的污染。
4、调节生态环境
美化城市景观推行种植屋面，有利于调节城市气候环境、减少雨水流失，抑制暴雨、风沙天气，改善城市景观，为发展居住生态环境，实现人与自然和谐相处，创建“花园城市”而造福于人民。
二、种植屋面防排水系统的设计与施工种植屋面的构造层次较多，技术要求也比较高，涉及建筑、农林和园艺等学科，是一个系统工程，必须从设计、选材、施工和管理维护等方面进行综合研究和处理。
为了保证种植屋面上的植物既能培育生长，又要防水和排除积水，做到不渗不漏，才能满足房屋建筑的使用功能。为此，其构造层次较复杂，各个构造层次都有自己的功能和作用，一旦发生渗漏现象，整个屋面必须翻工重做，不但工程量大，费用也较昂贵。故在设计时，应按屋面防水等级为一级或二级进行多道的防水设防，并做好防排水构造的系统处理。现将种植屋面各构造层次的组成、作用、选材和施工要点分别叙述如下：
1、种植介质种植介质是屋面种植的植物赖以生长的土壤层。要求所选用的种植介质应具有自重轻、不板结、保水保肥、适宜植物培育生长、施工简便和经济环保等性能。一般可选用种植土、草炭、膨胀蛭石、膨胀珍珠岩、细砂和经过发酵处理的动物粪便等材料，按一定的比例混合配制而成。其中草炭和发酵后的动物粪便可为植物生长提供有机质、腐植酸和缓效的基肥；膨胀蛭石和膨胀珍珠岩不但可以减小种植介质的堆积密度，而且是有利于保水、透气、预防植物烂根，是促进植物生长的材料，还能及时补充植物生长所需要的铁、镁、钾等无素，也是种植介质中PH值的缓冲剂和调节剂。
也可直接选用为种植屋面专门生产、成分及粒度配置合理，保水保肥、能够促进植物根系发育和生长，且堆积密度仅为450Kg／m3左右的人工合成的无机栽培材料作种植介质。
种植介质层的厚度应根据介质和植物的种类而定，一般草坪为150～250mm；小灌木为300～400mm；大灌木为500～600mm；乔木为800mm以上。
2、隔离过滤层在种植介质层与排水层之间，应采用重量不低于250g／m2聚酯纤维土工布作一道隔离过滤层，以起到保水和滤水的作用。其目的是将种植介质层中因下雨或浇水后多余的水及时通过过滤层排除出去，以防止植物烂根，同时可将种植介质保留下来，以免发生流失。
3、排水层隔离过滤层的下部为排水层，排水层可采用的、留有足够空隙并有一定承载能力的塑料排水板、橡胶排水板或粒径为20～40mm，厚度为80mm以上的卵石组成。其作用是将通过过滤层的水，迅速地从排水层的空隙中汇集到汇水孔排除出去。
4、耐根系穿剌的防水层众所周知，各种植物的根系均具有很强的穿刺能力，许多传统的防水材料都容易被植物的根系所穿透，而导致屋面发生渗漏。为此，在种植屋面中，必须在一般的柔性防水层之上，空铺或粘贴一道具有足够耐根系穿刺功能的材料，如高密度HDPE土工膜、低密度聚乙烯（LDPE）土工膜、聚氯乙烯（PVC）卷材、聚烯烃（TPO）卷材和铅合金（PSS）卷材等作耐根系穿刺防水层。
为确保植物根系不但不能穿透材料本体，也不得穿透材料的接缝部位，因此要求耐根系穿刺防水层的接缝均应采用焊接法施工，并须使接缝焊接牢固，封闭严密。对热塑性材料，采用单缝焊接时，搭接宽度为60mm；其有效焊接宽度不应小于25mm；采用双缝焊接时，搭接宽度为80mm，其有效焊接宽度为10mm×2＋空腔宽度，铅合金卷材的接缝，应采用的焊条和工具进行焊接。
5、卷材或涂膜防水层在种植屋面工程中，除采用耐根系穿刺的防水层以外，尚应在其下部再铺设1～2道具有耐水、耐腐蚀、耐霉烂和对基层伸缩或开裂变形适应性强的卷材（如聚酯胎改性沥青防水卷材、合成高分子防水卷材等）或涂料（如双组分或单组分聚氨酯防水涂料等）作柔性防水层。当采用卷材作防水层时，根据标准《屋面工程技术规范》和《屋面工程质量验收规范》的规定，应优先采用空铺法、点粘法和条粘法进行施工，但卷材的接缝以及卷材防水层的周边应满粘。
种植屋面的四周应砌筑挡墙，挡墙下部应留置泄水孔，泄水孔的位置应准确，并应与水落口连通，不得有堵塞现象，以便及时排除种植屋面的积水。
6、找平层为便于铺设柔性防水层，找坡层上应做水泥砂浆找平层。找平层应压实平整，待找平层收水后，应进行二次抹平压光和充分保温养护，不得有酥松、起砂、起皮和空鼓现象。
7、找坡层为便于迅速排除种植屋面的积水，确保植物正常生长，屋面宜采用结构找坡。当不能采用结构找坡而须用材料找坡时，应选用有一定强度的轻质材料（如陶粒、加气混凝土、泡沫玻璃等）做找坡层，其坡度宜为1％～3％。
8、屋面结构层屋面结构层应根据种植屋面的种类和荷载进行设计和施工，一般应采用现浇钢筋混凝土作屋面结构层。当采用装配式钢筋混凝土板时，应用强度等级不低于C20的细石混凝土将板缝灌填密实；在板缝宽度大于40mm或上窄下宽时，应在缝中放置构造钢筋进行加强处理，板端缝亦应嵌填密封材料封闭严密。
HDPE geomembrane used for roof root separation layer processing - used for roof root separation layerseepage control effect of root separation double
With the deepening of reform and opening up and the extent of the city continues to expand, the survival of the people of the city space is becoming smaller and smaller. In order to improve the city 's green coverage rate,improve zoology environment, beautify the city landscape, the implementation of the green roof is the mosteffective way to.
One, development of planted roof
Be imperative in the modern society with the rapid development of today, China's large and medium-sized cityland resource is the " gold ", can be used for green land area is less and less. However, hundreds of millions of roofing is bare, and make full use of this has yet to be green " open space " development of planting roof, be imperative.
1, the development of planting roof, slowed the city's " heat island effect "
Building surface temperature with time
Due to the various types of building roof, wall and road are the good performance of the " large accumulator ",their daytime absorption of solar radiation energy, night heat, resulting in urban night high temperature,leading to the urban temperature than suburban temperature 2～ 3 ℃. Because the temperature rise is partlyIsland, it called for " heat island effect ". If the roof built in planting roof, roof planting flowers, grass, trees, wide,through the roof greening, realize the " ping changed green ", not only can greatly improve the city 's green coverage rate, but also can effectively ease the city's " heat island effect ". According to the report, every hectare green day to absorb heat from the environment, equivalent to the 1890 power of 1000 Watts air conditioning effect.
2, the implementation of roof greening
Have the added benefit of city atmospheric oxygen content roof greening by plant photosynthesis, absorb carbon dioxide in the atmosphere, release oxygen, easy to maintain the carbon dioxide in air and oxygen balance, improve air quality, according to the determination, 24 square meters of bluegrass Ping, a day canmake oxygen 1380 grams, enough to supply an adult normal the 1 day of life need of oxygen; a beech daycan absorb carbon dioxide and produce oxygen 2352 grams, 1712 grams, played the role of air purification.
3, roof planting plants
Can absorb harmful substances, reduce atmospheric pollution roof plants with adsorption, fixed dust, heavy metal elements and atmospheric absorption of NH3, SO2, NO2, HF and CL2 and other harmful substances,and can reduce city noise function. According to the determination of the thickness of 120mm, plant insulation layer up to 40 dB, which can obviously reduce air and noise pollution.
4, regulation of ecological environment
Beautify the city landscape implementation of planting roof, helps regulate the city climate environment,reduce stormwater drain, suppression of heavy rain, sandstorm weather, improvement of city landscape, for the development of residential ecological environment, realize the harmony between man and nature, to create a " garden city " and the benefit of the people.
Two, planted roof drainage system design and construction of planted roof structure more, technical demand is high, relates to the construction, forestry and gardening and other professional disciplines, it is project of a system, must from design, material selection, construction and management of maintenance and other aspects of the comprehensive research and treatment.
In order to ensure the planting roof plants can not only foster growth, and waterproof and drain the water, dono leakage, in order to meet the housing architectural use function. Therefore, its structure more complexstructural hierarchy, each has its own function and role, once the leakage, the entire roof must rework redo, not only large quantities, costs are more expensive. Therefore, in the design, according to the roofing waterproofing rank for grade one and grade two for multi-channel waterproofing, and good drainage structuresystem. The planting of roof the structural hierarchy of composition, function, material selection and construction key points are described as follows:
1, the growing medium cultivation medium is roof plants grown in soil layer. Requirements of selected plantingmedium should have light weight, does not harden, water and fertilizer retention, suitable for plant cultivationgrowth, simple construction and economic and environmental performance. The general choice of planting soil, peat, vermiculite, perlite, fine sand and treated through fermentation of animal manure and other materials, according to a certain proportion of mixed and compounded. The peat and fermented animal fecesfor plant growth, and the effect of humic acid organic fertilizer; expanded vermiculite and perlite can not only reduce the growing medium bulk density, and is conducive to preserving water, ventilation, prevention of plantroot, is a plant growth promoting material, can replenish needed by the growth of plants iron, magnesium,potassium and other elements, but also the growing medium in the pH value of buffer and regulator.
Can also be directly used for planting roofing, specialized production, composition and particle size of reasonable configuration, water and fertilizer, can promote plant root development and growth, and bulk density of only 450Kg / m3 around the artificial synthesis of inorganic materials for plant cultivation medium.
Cultivation of dielectric layer thickness should be based on the medium and plant type, general lawn is 150 ～ 250mm; small shrubs from 300 to 400mm; large shrub to 500 ～ 600mm; arbor is more than 800mm.
2, filtration layer in a growing medium layer and drainage layer between, should use the weight of not less than 250G / m2 polyester fiber earthwork cloth as a filtration layer, in order to water retention and drainageeffect. It is intended to be a growing medium layer due to rain or watering after excess water through the filter layer in time out, in order to prevent root rot of the plant, at the same time can be a growing medium preserved,to prevent erosion.
In 3, a drainage layer filtration layer is arranged at the lower part of the drainage layer, a drainage layer may be used, leaving enough space and have a certain bearing capacity of plastic drainage plate, rubber drainage board or particle size of 20 ～40mm, thickness of 80mm over the pebbles. Its role is to be passed through the filtering layer water, rapidly from the drainage layer in the gap together to the drain hole out.
In 4, root of puncture of the waterproof layer as everyone knows, all kinds of plant root system has strongpuncture ability, many of the traditional waterproof material is easy to plant root penetration, which led to theroofing leakage. Therefore, in planting roof, must in general flexible waterproof layer, empty shop or paste aroot system with sufficient puncture functional materials, such as high density HDPE geomembrane, low density polyethylene ( LDPE ) geomembrane, polyvinyl chloride ( PVC ) membrane, polyolefin (TPO )membrane and lead alloy ( PSS ) membrane for root system puncture proof layer.
To ensure that the plant roots not only cannot penetrate the material body, also do not penetrate the materialof joint, thus requiring root system puncture waterproof layer shall be used for welding seam construction method, and shall make the seam welding firm, tight seal. The thermoplastic material, using a single seam welding, lap width is 60mm; the effective width of the weld shall be not less than 25mm; double seam welding,lap width is 80mm, its effective weld width of 10mm× 2 + cavity width, lead alloy sheet joint, used to be the toolelectrode and welding.
5, material or coating waterproof layer in planting roof construction, except the root of puncture of thewaterproof layer outside, still should be in its lower part 1～ 2 props are laying waterproof, corrosion resistance, mildew and primary expansion or cracking deformation adaptability of material (such as polyestermodified asphalt waterproof coiled material, synthetic high polymer waterproof coiled material etc) or coating (such as a two-component or single component polyurethane waterproofing coating etc. ) for flexible waterproof layer. When using the web as a waterproof layer, according to the national standard of " technical code for roof engineering " and " code for acceptance of construction quality of roof " provisions, should give priority to the empty shop law, point sticking method and adhesive construction method, but the coil joints andthe surrounding membrane waterproof layer should be full bonding.
Planted roof masonry retaining wall around should be lower, retaining wall should be indwelling drain,drainage hole position should be accurate, and should be communicated with water, no clogging, so as toeliminate the water planting roof.
In 6, a leveling layer to facilitate the laying of flexible waterproof layer, the sloping layer should do on cement mortar screed-coat. The leveling layer should be compacted to smooth, leveling layer water, should be two times the screeding press polishing and sufficient maintenance, there shall be no loose, sand, bark andhollowing phenomenon.
In 7, the sloping layer to facilitate rapid elimination of planting roof seeper, ensure the normal growth of plants,should adopt the structure for slope roof. When not used for slope structure and must use the material to find the slope, choose a certain strength of lightweight material ( such as ceramic, aerated concrete, foamed glass) do the sloping layer, the slope should be 1%～ 3%.
In 8, the roof structure layer of roofing structure layer should be according to the planting roof types and loaddesign and construction, should in general be using cast-in-place reinforced concrete roof structure layer.When the assembled reinforced concrete slab, application of strength grade of not less than C20 of fine stone concrete will be filled in dense seam; seam width greater than 40mm or narrow width, should be in the gapplaced reinforcement strengthening, plate end seams should also be filled sealing material sealing is tight.